How I Met Your Mother/WMG

Robin being the mother is still a possibility
Even after Ted and Robin broke up earlier in the series and tried to remain Just Friends their relationship went back to Will They or Won't They? off and on over the course of the series before Robin was with Barney. (And it still occurs even after Robin and Barney broke up and Barney has those issues with her as well.) Not too mention on how Ted and Robin have their promise to marry at 40 if they haven't already done so. Not too mention on the end of the 3rd episode of the 7th season in which Victoria walks away from Ted she states that Robin is the reason why none of Ted's other relationships over the course of the series worked out. Now you might be thinking "But Robin can't be the Mother since Future!Ted called her Aunt Robin" but that is because the show didn't want to reveal the identity of the mother already. (And lets be honest the show is not devoid of Fridge Logic over the course of the series.)
 * The deal they made no longer matters, as the most recent episode revealed
 * In the episode "Disaster averted", Robin is wearing a yellow coat, also visible behind various characters in screenshots. Significant?
 * While the "I met your mother at Barney's wedding" thing might be explained away as "seeing a heretofore unknown facet of Robin's personality," the information from "Girls vs. Suits" (i.e., being Cindy's roommate, having weird and whimsical musical/artistic tastes) clashes pretty strongly with what we know of Robin. Unless Word of God declares that a red herring of some sort, this theory seems pretty unlikely.
 * Actually plenty of the hints have been Red Herrings over the course of the series (Cindy's Roomate is Cindy's Lesbian lover for example). So we can't really rely on the "hints" anymore so one can't be too certain over who is going to be the Mother of Ted's children.
 * Um....Cindy's roommate was not Cindy's lesbian lover. Where the hell did you get that from? Ted just thought she was the roommate for a minute. She was the Mother. Unequivocally, absolutely, undeniably the mother. The ankle that Ted glimpsed was the Mother's. The items scattered around the apartment were the Mother's. The hobbies and descriptions Cindy gave were of the Mother. The umbrella Ted left was the Mother's, and the Mother got it back. The room he was standing in was the Mother's. This is all stuff that Future Ted explicitly told his kids. Yeah, lots of red herrings...but they're all explained away as teases or insinuations. Future Ted never outright lies. And Cindy's roommate was the Mother. That is one single fact that we absolutely know with total certainty.
 * She can't be: in the 12th episode of season 3, "No Tomorrow", Future!Ted says the mother was at the Saint Patrick's day party he went to; she was even the one who left the yellow umbrella he uses at the end of the episode. Robin was with Marshall and Lily at their new apartment while the party was going on, so it couldn't have been her.
 * Not to mention it's been revealed

The mother is Barney's Biological half-sister
Barney's father mentions that he has a biological half-sister in college. The Mother is known to be in college. Ted marries her, Barney marries Robin. "Uncle Barney" and "aunt robin" aren't honorary anymore.
 * Something from The Bro Code here: Article 19 mentions that a bro is not allowed to sleep with another bro's sister. Amendment 3 throws article 19 out the window, if the sister is a 9 or higher. Carly Whittaker is either really hot or not the mother.
 * This may be the most likely, as she is the only college student who could be at a wedding Ted will be at (that we know of).

Victoria is the mother
He met her at a wedding, didn't he? There is no indication that the wedding we see after Ted claims he met his wife "the day of the wedding", that he should have to meet her at THAT wedding... Victoria is also fan favorite of all of Ted's girlfriends (except for perhaps Robin of course, but we know that ship can never sail).
 * As i say to many of the WMGs, Ted didn't have his last cigarette two weeks into dating Victoria, this is a joss on many theories.
 * Damn! Did he say last cigarette two weeks into dating their mother, or after he met their mother? If it's dating, you can justify/handwave it as "after they started dating AGAIN"...
 * Aaaaaaand they're at least teasing it again in the seventh season.
 * Umm... no, they are not. It's explicitly stated that Ted meets the Mother on Barney's wedding. Also, even though March 17, 2008 ("No Tomorrow"; the mother is at the St. Patrick's Day party) is a couple of days more than 2 years after "Cupcakes" (March 6-ish, 2006; Victoria's departure), it's unlikely that Victoria's scholarship started at exactly the day she arrived to Germany. It will rather be a lesson about bad timing.
 * When people say, "Two years" they rarely mean, "exactly two years" or exactly 730 days. That's usually just a round estimate, maybe a little more or little less than two years, quite a bit more than a year and a half and quite a bit less than two and a half years. The exact date she left and the exact date of St. Patrick's Day isn't enough to rule it out.
 * Klaus doesn't exist. Victoria only claimed to be getting married because she didn't want to get involved with Ted while he's still in this "weird" everyday relationship with his ex-lover Robin and her other ex-lover Barney. When Ted noticed she wasn't wearing a ring, she made up the story of finding the ring in her boyfriend's sock drawer. When Ted asked her her fiance's name, she asked, "Whose name?" which is often an indication that a character is lying. She then said, "Klaus" either because 1) there was actually a Klaus in her class and his name was the first name that occured to her, 2) there never was a Kalus. She'd made him up while communicating with Ted in their failed long-distance relationship to get him jealous because she was justifiably worried about his close proximity to Robin, or 3) Ted's remembering wrongly that there was a Klaus in her class, and Victoria just rolled with it. Even if Klaus does exist, we have no evidence he's actually proposed to Victoria yet. In any case, Victoria's brief return isn't the definite Jossed Ship Sinking it looks like at first glance. Klaus didn't appear in that episode, and everything we know of him is from just one person, Victoria.
 * This is seemingly Jossed in the Season 7 finale (although Klaus still didn't actually appear...)
 * One final theory on how the "Klaus doesn't exist" idea could still be true. The wedding Victoria ditched to be with Ted isn't her own wedding, but the wedding of Cindy, the Mother's former roommate (and Victoria's if she's the mother). As to why she'd keep lying about this, she might've initially lied about getting married because she didn't want to get involved with Ted while he was still rooming with Robin, but after leaving Ted she realizes she still loves him, but feels she's now stuck with the lie, especially when Ted calls her on the day she's wearing a wedding dress.
 * ... why would she be wearing a wedding dress then?
 * With Klaus out of the way (this is the same troper who made the "Klaus doesn't exist" theory above), here's how the Mother could still turn out to be Victoria. It would be perfectly natural for Vicotria to be at Barney's (and Robin's?) wedding, since she makes outstanding wedding cakes. It's possible she and Ted will agree that the time they truly "met" would be when Ted's finally free of his "weird" Barney/Robin entanglement (that Future!Ted affirms Victoria's right about) and he's ready to be fully committed to her. While this could theoretically apply to any of Ted's ex-girlfriends, Victoria's the only one quirky enough (with her "One Night Only" "Drumroll" when she and Ted first literally met) for it to be perfectly in-character for her to agree (or even come up with) the idea that this will be the time they "met".
 * Modified as of the Season 7 finale, where Ted and Victoria ride off together. Viewers have often debated whether the Mother should only be seen in the final episode or if we should have a full season devoted to her relationship with Ted. With Vicotria as Ted's girlfriend at the start of Season 8, it's possible to have both, with fans arguing whether she'll be the Mother. I can even imagine Ted and Victoria breaking up at some point in Season 8, only to get back together at Robin and Barney's wedding. Her presence there might even be deliberately arranged by Robin/Barney/both to try to get them back together. In that case, Ted and Victoria could decide they truly "met" when they got together and stayed together.
 * It can't be Victoria, as the mother is a college student who started college when Victoria was in Germany.
 * You are incorrect. Victoria went to Germany for two years. She left in late Season 1, March, 2006. Ted mistakenly went to the Economics classroom in the Fifth Season Premiere, September, 2009, three and a half years later. It's at least possible for Victoria to have gone to Germany, stayed there for the full two years, then for whatever reason, taken an Econmics class a year and half after she got back.
 * Wouldn't Ted have recognized her if she was in that class?
 * The classroom was a big, crowded auditorium. Victoria could've seen Ted before he could've seen her and done something like scrunch down behind her laptop to keep from being seen.
 * Seemingly Jossed by the seventh season finale. Ted and Victoria ran away ran away together, but since they got together well before Barney's wedding, it really can't be Victoria.
 * Of note is that this is still "the day of a wedding," but it's not Barney's, obviously.

Ted's future wife is a brunette, or at least can't be a blonde
When dating Elliot Reed, We get a brief glimpse of what the future would be like if Ted had married her. Cue Ted telling his children how he met their mother. In this alternate future, BOTH children are blonde. Given that Ted's a brunette and blonde is a recessive gene, Ted needs to have one brunette gene and one blone gene. Seeing as both his children would end up being blondes, and in real life they are both brunettes, this should indicate that the real mother isn't a blonde, and probably should be dark-haired.

Though, of course, the genes are the loophole to this theory - Ted could very easily be married to a blonde en still get infinity brunette children. But, seeing as how this show likes to play with very subtle hints, this seems as good as any.

Barney's half-sister is the mother.
When Jerry shows Barney the picture of his family, he points out his daughter Carly but we never actually see her, in the photo or at the family dinner. What we do know is that she's in college, which means she could be Cindy's roommate and may have been in the Econ class. And she probably lives in or near New York to be close to her family. Plus, how supremely ironic would it be if Ted marries Barney's sister after Barney tries so hard to hook up with Ted's?
 * And if Barney gets married, Ted would be best man, and the sister would most likely be at the wedding.... Two plus two.
 * It seems like a Red Herring which might actually mean that it isn't and viewing it as a Red Herring is the actual Red Herring part of it. Yeah.
 * Interestingly, it would literally make Barney "Uncle Barney" to the kids, and Robin "Aunt Robin" if she's who Barney marries. Marshall and Lily would still be faux-family, of course.
 * If the season finale of Season 7 ("The Magician's Code") is anything to go by, we may be seeing Jerome and his family again. Put two and two together...
 * If the season finale of Season 7 ("The Magician's Code") is anything to go by, we may be seeing Jerome and his family again. Put two and two together...

Barney or Robin already knows the mother.

 * And she will come to their wedding, and meet Ted. While Ted goes off on tangents constantly, the overall story arc has always stuck to the concept that everything was significant: Ted dating Robin leads to their breakup, which leads to him getting the tattoo, which leads to him meeting Stella, which leads to him getting the job at the university, which presumably leads to him meeting the mother.
 * But now, Robin and Barney's relationship is the A-plot of most episodes. This only makes sense if the story of how Barney and Robin got together, and grew to want a conventional relationship, is related to how Ted meets the mother.
 * Though we still never know
 * If either of them knew a girl well-suited for Ted, wouldn't they have arranged an introduction years ago (if only to avert the endless cycle of drama resulting from Ted's active attempts to find love)?
 * Not necessarily. Remember "The Scuba Diver"? Lily had a woman "on hold" for Ted for years because she didn't think he was "ready" yet. To be honest, her explanation did seem utterly forced but... well, it's not without precedent. Plus, it could be someone that is currently in a relationship, thus they wouldn't set her up with Ted.
 * Not necessarily. Remember "The Scuba Diver"? Lily had a woman "on hold" for Ted for years because she didn't think he was "ready" yet. To be honest, her explanation did seem utterly forced but... well, it's not without precedent. Plus, it could be someone that is currently in a relationship, thus they wouldn't set her up with Ted.

He meets their mother

 * Ted meets the kids' mother and conceives them.
 * Impossible. Get out.
 * I think you mean "inconceivable"...
 * You Keep Using That Word

Ted is their Mother.

 * The show is his explaining to his children how he invented, or encountered the person who invented, the technology for male pregnancy.
 * And that person would be Barney.
 * If this is the correct theory, it has to be Barney. But Barney should be the "mother" because Ted can't meet himself.
 * "Kids the thing you have to know about Uncle Barney..."
 * Is that he's actually your mother?
 * And thus the children were given massive complexes.

This show is one of those where the Last Girl Wins.
In the series finale, the mother (who has previously never appeared in the series) will walk in on whatever is happening, Future Ted will say "And that's how I met your mother", and the series will end. We know for sure that their mother is not one of the characters Ted has met because, well, it's not called "How I Decided To Marry Your Mother."
 * So, everything up to that point will have effectively been a Shaggy Dog Story? Yes!
 * Except from when you tell about how you meet your significant other, you tell about the first time you meet, your first date, et cetera. Ted just has a huge amount of backstory.

Barney's "stalker" is Ted's future wife.
When Barney was being "stalked" by a woman telling his prospective dates that he was a jerk, they never revealed who she was. They only showed her from the back, and all we know is that she has blonde hair. At the end of the episode, Future Ted says to his kids that "Barney eventually found out who she was, but that's a different story." This still hasn't been resolved, so it's fairly obvious what the resolution will be.
 * It was revealed that it was Britney Spears.
 * So, Britney Spears is Ted's future wife.
 * NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!

Lily's teacher friend Jillian is the Mother
It was in the 4th season episode "Woo!" where we were introduced to Lily's friend Jillian. Jillian seemed to have met the entire gang EXCEPT Ted. It had been stated in episodes before that both Lily and Robin played a big role in the meeting of the Mother. Robin had become a bit of a Woo Girl, and Lily works with Jillian. Also, there's the Woo translation for Jillian which said, "What if I never get to be a Mom?" And she's a brunette, just like Ted and his children. Just some things to think about.
 * Except at the end of the episode Jillian called "that Ted guy" cute, so she obviously met him, however briefly.
 * This actually might work (at least from the standpoint of matchmaking). Jillian, when not woo-ing it up, was smart and loved her chosen field (much like Ted), and her woo-translation seems to echo Ted's own concerns and long-term desires. Also, "brief introduction while at least one of us was plastered" does not necessarily equate to "meeting." If they do get introduced at Barney's wedding, which would be years and years after a brief encounter during one drunken night in a long string of drunken nights, it would be a de facto "first meeting."
 * Jillian is a teacher at Lily's school. In The Leap we find out the Mother was in . Therefore, Jillian can't be the Mother.
 * Not Jossed. People all the time.
 * But it's unlikely that a 2nd grade teacher would have the time to.
 * Plus, why would a second grade teacher need to ?
 * Two possible answers? Jillian.
 * If Jillian did go to college, why would she live in student accommodation? She would already have a house and money saved up.
 * The mother doesn't necessarily live in student accommodation, she just happens to have a roommate.

The Mother is a waitress at the bar.
Every episode of the show is supposed to be part of a story about how Ted met his children's mother. But the episodes don't have much in common - except that almost all of them have a scene in the same bar. Therefore it's a story about how Ted met their mother there.
 * Jossed because she will be in his class the next season, and it is explicitly told that without him lecturing this class he wouldn't have met her.
 * The reason he wouldn't meet her without lecturing his class is because she was in the Econ class he walked into on his first day.
 * That josses a detail, not the theory.
 * Except the show's title is "How I MET Your Mother", not "A Bunch of Random Stories Connected by MacLaren's Bar, Oh By the Way Your Mom Worked there All Along." Perhaps she could become a waitress there at some point, but Ted would not have told such a long story to his kids otherwise. Plus it's been stated that Robin was instrumental in meeting the mother, and Ted and co. have been going there since before they met her, and the producers set up each season so that idea of Robin being essential to meeting the mother could still stand up if the show got pulled suddenly. Future Ted just tends to ramble on and get distracted by unrelated stories.
 * Completely Jossed as of "Garbage Island".

Tony's movie plays a key role in meeting the mother
In "Right Place Right Time", Future Ted goes on and on (and on) about how the events of the episode lead to meeting the mother. He runs into Stella at the end of the episode. We know she's not the mother, since we see different children when he talks about what things would have been like if he married her. Moreover, in the very next episode ("As Fast As She Can"), he helps fix her marital problems with Tony and they're put on a plane to California.

However, we know that Tony makes The Wedding Bride, which is released in May 2010. You know, around the time the season finales happen. At the end of "As Fast As She Can", Future Ted promises to tell the story of that movie. It could be concluded that Ted meets the mother at a showing of the movie, or while renting the DVD.
 * I had interpreted that little aside as meaning that the movie would actually be based in some way on Ted's life. Probably even based on the relationship between Tony and Stella, the title coming from Stella leaving Ted at the altar.
 * Jossed. That meeting led to her husband getting him thinking about a teaching job, and he's stated that the mother was in that class.
 * However, in S7 Ep!& No Pressure, the movie theatre is billing The Wedding Bride III. Ted mentions the movie they wanted to see was sold out. Again, though, this is only the first time Ted professed his love for her, but in the grand scheme of things this would play a part in the Mother becoming the Mother.

We will never see The Mother.
The series will end with Ted about to walk up to an offscreen woman and give her umbrella back.
 * In "Girls vs. Suits"

The Mother's name is Tracy.
In the first-season Thanksgiving episode, FutureTed has to tell his kids that he's joking after saying that the stripper who offered him a lap dance was their mother, which means introducing herself as "Tracy" didn't clue them in.
 * Obviously there are a whole host of ways this could be wrong, from Ted not actually narrating the dialogue word-for-word to the kids being too shocked by the stripper thing to point out that the name is wrong. But it still bears mentioning.
 * Or perhaps the kids thought Tracy may have been a stage name.
 * She had given Ted a fake name, then (after he did nothing but tell her his name, which set up for the joke in his next line) immediately game him another name in a Stage Whisper. There's no reason to believe she told him her real name right there in the main area of the strip club.

The mother will be played by Summer Glau.
We saw her feet. Summer Glau has feet. Boy, does she have feet.

The Mother is Ted's "Perfect match"
In the episode "Milk", Love Solutions finally found him a girl. We don't see her and her face on the photos is blurred. Now seriously, why on Earth would the creators go on such lengths to obscure her identity if she was just a girl? If she was only a one-shot character, she would probably have been shown (and Barney would probably have banged her pretending he was Ted). Solution: she is the mother and the creators haven't found the actress to play her yet.
 * Her face on the photos was blurred because Ted has no idea what she looked like. You can't remember the face of someone you've never seen. If you want a Doylist reason for the blurring, it's probably not the same person in all the photos.

This season Ted will finally meet the mother.
But it will turn out that the mother hates Ted for some reason and the show's name will switch to "How I Won Your Mother".

The mother is going to be a massive letdown
Because with this level of build-up, how could she not be?
 * Does seem very likely, but if they do it right it could work. One of the reasons Girls vs Suits is one of my favourite episodes (Aside from the song) is Ted finally tells us what made him fall in love with the mother, such as painting transformers and singing show tunes to muffins. If they focus on that rather than making her a Relationship Sue, we'll be good.

The Mother is the Mother.
Just to add some horror to this WMG page...
 * Considering it, it's funny that Ted is an architect and the Father from Dragon Age Awakening also calls himself The Architect.

Robin is the one who introduces Ted to the mother, or is in some way essential to when they marry
That's why the story starts with her and also when they dated. Either Robin is how they meet or she gives Ted advice while he's dating the mother, or gives her advice on what to expect from Ted. She may also be the one helps to fix up a big fight or something.
 * The story begins there because that's the night he decided he was ready to get married. It just happens to coincide with the night he met Robin.
 * Or it could be both.

The Mother is the girl Ted bumped in to at the St. Patty's day party.
Think I'm on to something. a) She's at the party and b) I'm pretty sure she had a line in the episode, extras with speaking parts get paid more that's why they generally don't speak. Why have her speak if she's not important? Why have Ted bump in to someone at all?
 * This is the going theory so far: sharp-eyed viewers have noted that her outfit matches the one worn by the woman in line with the yellow umbrella.
 * Word of God: a Red Herring.
 * When did Bays & Thomas say that?
 * Ted states that he never met the mother that night because she probably would've hated him. Therefore, Word of God.
 * ... how is that Word of God?
 * At the end of 'No Pressure' a bunch of girls with yellow umbrella's walk past Ted - the first one that passes him is wearing the same hat as The Mother was at the beginning of the episode and while it's too blurry to tell for sure from what I can see she looks a lot like the girl that Ted bumped into...

Ted gets the mother pregnant on the first date
They will most likely hold off introducing the mother until the last season, possibly towards the end of that season. And it has been stated that the series will last 8 seasons in total, meaning it will end in 2013. By my best estimates the kids are around 15 and 16 in 2030 meaning that the oldest was born in 2014. So if the show does wait to reveal the mother until the end, there won't be much time for a courtship and marriage. So Ted will probably meet the mother, fall madly in love with her at first sight and then get her pregnant on the first date. This would also explain why he finally quit smoking two weeks into dating her. He found out she was pregnant and decided to give up smoking for real because he is going to be a dad.
 * Seeing as Ted will meet the mother at Barney's wedding, and it's very strongly hinted that his wedding is in season 7 (possibly, even probably, the finale), they're probably going to give the mother some development and some sort of romance arc with Ted during season 8. However, this still doesn't leave a whole lot of time for them before mid-2013 (the latest estimate for the daughter's conception if we lowball her age) which would take place around the end of season 8. It would be unsatisfying for Ted and the Mother to rush through engagement, wedding, and kids that fast for no reason (especially given what happened with Stella), so the best way to forcibly shorten the pre-kids story enough to make the daughter's age plausible would be for Ted to knock her up before they get married...though perhaps not before they get engaged. And Barney's wedding can't take place before June 2012, because Lily's not pregnant in the flashforward to his wedding, and since she conceived at the end of August, her due date is in late May-to-June.
 * "Trilogy Time" reveals that  Assuming that the dates in universe roughly match the dates IRL, Trilogy Time happens every three years around April. Therefore,   If Barney's wedding takes place in 2013 (in May, around the time of the season finale, at the latest), there is still enough time for Ted to date the mother for about a year, marry her and get her pregnant soon after. Or get her pregnant and then marry her, but definitely not during their first date.

Ted actually marries Zoe.
But it's discovered that Zoe is infertile. Still Zoe and Ted both still want to have kids, so the person Ted meets at the wedding is the "mother" who is artificially inseminated with Ted's sperm. Thus, Zoe can be Ted's wife and the "mother" has not been met yet. Furthermore, the reason The Captain divorced Zoe was because of the infertility.
 * Jossed. In a flashforward/back Ted tells the waitress from Mc Claren's that it ended pretty badly between them. Now we've just gotta watch and find out how.

The Mother is Nora
Nora is a little like Robin but a lot more romantic at heart. She is also seen wearing yellow (which seems to be a color motif for The Mother), hasn't been grandly introduced like others have been (i.e. Zoey, Victoria, etc), Robin does play a pretty big role in the whole meeting of the Mother. So my theory is that Barney and Nora do date for a few, but during that time, he realizes that he actually still loves Robin. After a while, Nora and Barney do remain friendly for the most part and she is invited to the Barney and Robin wedding where Ted finally meets The Mother. Also I think it'd be interesting that Ted saw Robin first and fell for her but she ended up dating Barney so Barney meeting Nora first and all would be really interesting sort of reversal.
 * Jossed. Nora and Ted met at Mc Claren's, not the wedding.
 * Nora marries Barney: He has not lost interest in her, and there's no way Ted wouldn't be his best man.
 * Except that Barney sleeps with Robin, figures out that she's his soulmate and breaks up with Nora. And we still don't know who the bride is.

The mother is Barney's half-sister.
They're both in college, and... that's pretty much it. Barney really is Uncle Barney, it's not just an honorary title like with the others, and after the wedding they really are bros. And Barney would hold it over Marshall's head forever as a reason why he's Ted's real best friend.

The Mother is in the bump girl scene
She's not the girl Ted bumped into, but a girl in the background, my personal vote is the girl who looked towards the camera and walked away.
 * While the bump scene would be meaningless without the mother in it, the bump itself seems like a Red Herring.

The Mother's name is Tori

 * This is based on my theory that there is also one more Robin Sparkle's song to come:
 * In the song "Let's Go to the Mall" the opening lyrics are, "Come on Jessica, come on Tori... Let's go to the mall, etc." We've already met Jessica Glitter back in "Glitter" so it would make sense that at some point we will meet Tori.
 * Ted will meet her at Robin's wedding, which will be to ugly-shirt guy that was introduced in the Season 6 episode, "Hopeless." As we know, Ted will be the best man, and it would make sense for Robin to introduce him to significant people from her past.

The Mother's name is Miriam.
Hi, Mym!

The Mother will provide the series-ending recap.
She tells the kids how Ted's life and hers were inextricably intertwined from her side of things, tying together the Foreshadowing from throughout the series... In about five to seven minutes, of course.
 * Or, alternately, her recollection will be even more long-winded. The last words of the series will be "how I met your father."

The Mother will be played by Jewel Staite.
There have already been an incredible number of appearances from Whedonverse alums on the show: Alyson Hannigan and Neil Patrick Harris in the main cast and Alexis Denisof, Morena Baccarin, Tom Lenk, Danny Strong, Amy Acker as guests. How great would it be to have Kaylee as the mother?
 * Alternately, it's Sarah Michelle Gellar.

The mother is Blah Blah.
Ted was just messing with the kids by telling them he didn't remember the name of the girl he was telling the story about.

We've already seen the mother
In the episode "No Tomorrow", Future Ted confirms that the mother was at the club that night - it's the girl that Ted runs into, excuses himself for doing so, and we never see her again... ...well, until the obvious, obviously.

Ted will lie or has already lied about the Mother's name.
And thinks that his kids are getting bored and might cut him off if they realize the story is going on longer than strictly necessary.
 * That sounds like a certain other romantic comedy....

Barney's cousin, Leslie, is the Mother
Leslie from "Okay Awesome" shows that Leslie
 * goes to clubs - The yellow umbrella was found at a club
 * did not meet Ted at that time - therefore she is a candidate for Mother-hood
 * is Barney's cousin - therefore would probably be invited to the wedding
 * would make the "Okay Awesome" story *so* much funnier

When Ted says he met the mother at a wedding, he is speaking figuratively.
The mother is either someone he already knows, but not well (such as Nora), or someone he was introduced to briefly in the past (such as Lily's teacher friend Jillian). "Meeting her" means that he started really getting to know her at/after the the wedding, or that he had the kind of perception-shift that made him view her as a potential romantic partner.

The Mother is one of Robin's friends that she was hanging out with in the Pilot
This group of friends is brought up on the first episode and then never seen again. The only purpose they seem to have is to give Robin an excuse to throw a drink in Ted's face and cut their time short. Plus it makes sense as to why they would be at the wedding (this theory makes more sense if Robin's the bride).

Whoever the Mother is, she will be the one to propose to Ted
Not only would it be a pretty hilarious way to end a series about a guy who is determined to find a wife, but it will basically allow things to be a total surprise to the audience. The series can really only end with either Ted in a relationship where he eventually proposes (little to no suspense) or he simply meets some woman and ends it with "and that, kids, is how I met your mother" (which just feels cheap). If he's the one proposed to, it allows him to have at least several potential women chasing after him while he decides, and just when you think he's made his decision, BAM, he gets proposed to.

Either Barney or Robin will be the one to introduce Ted to the Mother
I'm calling it now - Season 7 will end with either Robin or Barney tapping the Mother on the shoulder and saying "Haaaave you met Ted?"

Quinn the Stripper is both Barney's Mystery Bride and The Mother
And Ted doesn't actually meet her until Barney's wedding.
 * Ted has at least seen Quinn, if not met her, at the Lusty Leopard where she works. She could still be the bride, but Future Ted doesn't refer to her as "Aunt Quinn" in the voiceover. Doesn't discredit that theory though, considering the sentence her name was mentioned ("Barney met a girl called Quinn" would be valid even if she were Aunt Quinn).
 * Jossed. Ted meets Quinn properly (as in, actually talks to her etc.) at a dinner held by her and Barney.

Since Robin hurt Barney, she's going to have to apologize and win him back.
Then she'll propose to him, and is thus The Bride!

Ted never met the children's mother.
Rather, he kidnapped the children from a random house and took them back to his house to tell them a story about his now dead friends. The children are playing along because they know the police are on their way.

The Mother will be a Scrappy.
Because the writers dont have a good track record when it comes to the main cast longer relationship partners,
 * Ted: Stella became one when . And Zoe is a Relationship Sue with jerkass moment with her  . And this happen when they d became a couple.
 * Robin: Don is another Relationship Sue with all the gang saying how perfect he is for Robin. Even though the first time he showed up he was a jerk.
 * Barney:.
 * I'm not sure I agree... While Don and Zoe definitely count, Stella only became a Scrappy after they broke up. While they were together she was pretty well-received. Plus you're overlooking Robin herself, as well as Victoria. And Kevin was quite well-received as well. And I think you're playing Quinn's scrappiness up...

The mother drives a silver Toyota Rav-4.
One has shown up in the background for a disproportionate number of shots throughout the seasons. Logically, probably just a stock car they have on the set, but who knows, the show is pretty much Continuity Porn incarnate.

No matter who the mother is, at the end of the series Future!Ted will get a major calling out for how inconsistent and drawn out the story was.
This will most likely be done by the children, but certain other characters such as the Mother will probably participate in this as well.
 * Barney, Robin, Lily, and Marshall will all be there and reveal that Ted made up a lot of the story to be dramatic. there was no GNB, Marshall went back to the same company he originally worked for with Arthur as his boss. the company is either Altrucell or was bought by Altrucell. Barney didn`t sleep with over 200 women and always kinda wanted to get married but didn`t think it would happen so he hid behind his womanising personality. Ted didn`t have a crush on Robin when he first met her and they did not live together for more than a year (are we really supposed to believe that they couldn`t live together peacefully while they were dating but after the breakup they lived together for years)Future Ted doesn`t want to talk about her moving out because it was too painful. Lily and Marshall broke up for a longer time than depicted and it was much more tramuatic (notice how they frequently ignore that it happened and say they`ve been together since first week of college) and they were trying to have a baby since the begining of season 4 but kept having fertility problems. the story of how Ted met the mother is actually very simplistic and would`ve happened with or without the yellow umbrella or her being in the economics class he stumbled into. we all know Ted wouldn`t let the truth get in the way of a good story.

Ted's kids' names are....
Luke and Leia. Or Leah. Either way, it would be an homage to Ted's love for Star Wars (Marshall: "Ted loves Star Wars. He watches it in sickness and in health, in good times and bad, etc...) and when told to "swear on his unborn kids", he says "I swear on Luke and Leia". Given how Ted's ideal woman is practically himself, the mother would probably be fine with naming the kids Luke and Leia. Of course, the kids would never forgive them.

Bob Saget is how Ted hears himself
People hear themselves differently then others do and the future portions are from Teds POV therefor the deeper voice is how Ted hears himself

The kids from the future are androids.
Ted doesn't really want kids. He just loves the idea of the perfect romantic fantasy, where he marries a beautiful woman and has two beautiful kids and a beautiful dog who all live in a beautiful house that he designed. At some point in the future, he gives up on the whole "perfect" thing and decides that having real kids would be a lot of work, since he doesn't have a bride to share the raising of two kids with. So, he has a pair of robot kids created. It's not considered unusual, since having androids is the 2030 equivalent of playing The Sims.

He then fills in their memory so that they have more than just the basic programming of human behaviour. He has to input the data the old fashioned way so that they will "learn" from it the same way as a human child would. They will pick up behavioral patterns based on their "father" and his friends. He lives with Robin, Marshal and Lily as well as the woman who built his kids. She is now a close friend, having joined the group the same way as Robin did. Barney still has an anti-relationship apartment somewhere else but close-by.

The story of how Ted met their mother is really the story of how he met and got to know the woman who would build them, so we have at least two decades left to go.
 * Well, the mother does like to paint robots playing volleyball... oh my God...

Ted isn't really the father.
Ted isn't really the father of the two children. After he meets their mother, they become really close, and he becomes like a fake uncle for them. Ted could technically get married to anyone on the show.
 * Ted doesn't even say that he's married to their Mom. Could be that Robin is their step-mom and they just call her 'Aunt' Robin because she's so uncomfortable with the idea of having kids.
 * He does mention their wedding at one point.
 * It is also stated that Robin eventually made her peace with children. As well, the kids seemed shocked and appalled that Ted and Robin had ever been a couple.
 * They call him dad in the second season opening when they complain that it feels like he's been telling the story for a year and ask him to skip ahead. Given modern (and postmodern) family dynamics, though, that doesn't discredit this theory at all.

The Children are adopted.

 * In a surprise twist, Ted isn't the children's biological father; he adopted them from a woman he meets very briefly.
 * Alternately, Ted and their mother were never even involved. He just babysits because he is the only person in the group who has no life (aside from Barney, who dies, see below), and the Honorary Uncle titles were from their mother's friendship with the group.
 * Alternately, they're Lily's and Marshall's, who dies in a car crash between the end of the series and the "present" in the framing sequence. "Met" is a metaphor for "came to know and understand", and How I Met Your Parents would give away that he's not their dad. Ted and Robin take care of the kids, with the occasional help of Barney, who settles down somewhat (but not entirely).
 * They couldn't be Lily and Marshall's kids. Ted told the kids how Marshall opened Lily's letter that was supposed to be opened after her death "last year," as in a year before Ted tells the kids the story, so why couldn't he just call them "your mom and dad"? They would know who their parents were in that case...
 * But even then it's a dead end for this theory because Lily turns out to be just fine, not dead.
 * They are called aunt Lily and uncle Marshall many times in the stories, so Jossed.
 * Not necessarily. Looking at the simple structure of the title only tells how Ted met the mother of the kids. That would like me saying to you, "Did I tell you how I met your mother?" This is not "How I met your mother, fell in love with her, married her and had you two little bastards." Which leads me to...
 * They call Future Ted "dad" at least once. Like in the second episode, where Ted tells Robin he loves her, and his daughter goes "oh, Dad..."
 * And in the Perfect Week episode, he asks them in the end if he's a "bad Dad", so Ted's definitely the father. We have proof!

The biological mother of the children and the woman Ted marries may not necessarily be the same person.

 * As mentioned earlier, this is a story about how Ted met the mother of the two kids in the opening scene. This is not "How I met My Wife." This leads to several possible scenarios:
 * (The Most Obvious) Ted's wife is the mother of the children
 * Ted and his wife are unable to have children and this is how they met the biological mother of the kids
 * Ted's kids are not biologically his, but this is how he met their mother, which could be
 * His current wife
 * His ex-wife
 * The woman they view as a mother figure
 * This seems Jossed as of "Girls vs. Suits." Future Ted says

Ted has been dead for years.

 * The man telling the story to the children is obviously not Ted - their voices are completely different. But he's representing himself as Ted in the story and pretending to be the children's biological father. The easiest explanation is that Ted died when the children were very young, long enough ago that they have no real memory of him. Their mother married the story-telling man soon afterwards and convinced them that he was their father, either to spare them trauma or for some more sinister purpose. Robin, Marshall, and Lily are in on the deception too, as the children have met them without the secret being revealed.
 * In the fifth episode of season 3, we see Ted alive and well during the mid 2020s, when the children would have been about ten; and the photo in the den which is described in the 3rd episode of season 2 has the Ted we know and love. If Story Telling Man isn't Ted, then they should have noticed.
 * This theory has been Jossed. Word of God says they'll never pull something like that and the person telling the story in 2030 really is Ted.
 * "Ted Mosby...architect." Hey, there's precedent.

Future Ted is hallucinating.

 * Ted never fully got over his feelings that he and Robin were soulmates, and as time passed he purposefully sabotaged every relationship he was in (cheating on Victoria, inviting Stella's ex to their wedding, etc.) because he knew he was meant to be with Robin. As the years went on he developed severe emotional problems because of this and became a reclusive architect designing grand tributes to Robin secretly in his buildings. Finally as he succumbs to his long untreated mental illness(es) he creates what he believes Robin and his children would look like, and as a coping mechanism meticulously explains everything he could have, or should have, done to keep Robin instead of pushing her away from him. The series will end with his children revealing to him that they are figments of his imagination and that he has to face reality, and the camera pans to see Future Ted putting a shotgun in his mouth and then whispering "reality..." before a cut to black and the end credits roll.
 * Wouldn't that make Robin the (imaginary) Mother, which we already know isn't so (as she's 'Aunt Robin')?

By the time the story is told, Marshall is the President.
Marshall's law school buddies include a future senator and an Attorney General, two different people. If two throwaway characters get such good jobs, then a regular has to get something even better.
 * Along with dead Barney, the two most probable theories yet.
 * Heck, this explains why they got those good jobs - they went to law school with President Eriksen!
 * Wasn't one of them also Chief Justice of the Supreme Court?
 * That would also explain how Marshall gets access to Time Travel!
 * Future Marshall DID have a snazzy office...
 * ...oh god.
 * They did go to Columbia Law School after all.
 * That would explain how he eventually managed to save the planet (as Ted mentions in season 7)

Barney is dead when Future!Ted is telling the story
This theory comes from a highly observant fan. Considering some of this evidence and the vagueness of his job, in which the only evidence known is that he works with North Koreans.... it could be possible.
 * His womanizing also suggests that he's unlikely to hit a ripe old age.
 * One of Barney's most important character traits is that he always wears a suit. The Livejournal link talks about this suggesting mourning colors and the formality of a funeral, but there's a simpler link. If a man Barney's age died, how would the corpse be dressed in the coffin? Just like Barney is now - in a suit.
 * But from Barney's point of view, suits resemble joy and awesomeness, not death. This is why he never wears his suit in funerals. And anyway, he wants to be buried naked.
 * Barney is so cool that he is probably Too Cool to Live.
 * It's still possible, but Ted recently gave a date for when Barney finally quit smoking that was well outside the likely running time of the show. So he may die, but not in the present.
 * When I saw that episode, I thought immediately of this theory - what if the date given for Barney's last cigarette is the date of his death?
 * I'm sure I'm not the only one who imagined Barney with a cigarette in his mouth and a blindfold on with his back against a wall. Pretty sad, but almost plausible.
 * Especially suspicious is that Barney's life after the series is almost never mentioned. Future ted talks about Robin, Marshall and Lily all the time, but Barney is barely ever mentioned. Chances are the Barney is naught but a distant memory, for one reason or another.
 * Still, Barney is always referred to as "Uncle Barney" when Future Ted is talking to his kids, implying that Barney was at least alive until some point after the kids were born and were old enough to remember him. If the kids never knew him, why would they call him "Uncle"? And Ted would just refer to him as "my friend Barney" or some such thing, as he does for the other people in his life that his kids presumably never meet.
 * Not necessarily. The reason he's Uncle Barney isn't because he's close to the children, but because he is Ted's brother. As long as Ted considers Barney his brother, he's their uncle. I still no longer think this WMG is true, but for other reasons.
 * After recently watching season six's 'Subway Wars' again, I've found at one point Future!Ted says "To this day Barney denies this is what happened ... " (It's paraphrased, but he definitely says "to this day".) I think it would therefore be fair to say Barney is alive by 2030, because if the writers had been foreshadowing his death all this time, they would have had the line differently, like "Barney always denied this is how it happened, but ... " for example.
 * Also, "Tick, Tick, Tick" has Barney and Robin both swearing "to this day" about the song on the boat.
 * More than that, Barney seems to be very sure of who might cause his death. While his job is unclear, he seems to be very positive that he only has it because he knows a lot of dirt on the company. When asked if he was worried about being fired, he said "The things I know about this company, I can never be fired. I might find myself ashore with no fingerprints or teeth, but I can never be fired."

Barney is alive...
...but the kids don't know him well because he's been out of the country for several years. Despite his self-centred persona, it's pretty obvious that Barney actually likes helping people - as Hippy Barney he was going to join the Peace Corps, and even as his suited-up self, he does a lot for others, particularly his friends. Maybe Barney does eventually take over the evil corporation he works for, but as soon as it becomes Barneycorp, he starts some legen-DARY world-saving projects. Because of this, Barney has spent several years travelling between projects to supervise them personally, and to fulfill his dream of hooking up with a girl from every country in the world.

Barney disappeared from Ted's life sometime after The Kids matured and got to know him.
The Kids appear to be about 15, so it's entirely plausable that when they were five or six Ted and Barney just kind of drifted apart. Barney continues to be an honorary uncle because that's how the kids know and remember him, even though he hasn't been around for a while.
 * Unlikely, since Ted talks about Barney as if they still talk on ocassion. In Subway Wars, he says "To this day your uncle Barney won't admit it..." and in Tick, Tick, Tick... he says "To this day Robin and Barney both swear this is the song they danced to on that night." They also meet up at least twice a year for Thanksgiving and Robots vs. Wrestlers, so Ted and Barney are presumably still quite close.

Ted is telling this story to his wife's grave.

 * This is how I see the whole series ending. He does get married, but his wife dies prematurely, and he stands there relaying the story of how they met in the way he'd planned to tell their kids. Then robin comes up, tells him he's been here for hours, and they walk off.

Ted meets the mother of the children after the children were born
But soon enough so that they think he's their biological father. Alternatively, they know he isn't their biological father but in 2030 he's been around long enough for them to call him dad.

The mother is dead by 2020.
This is why Ted is telling the story himself, and in such great detail, without any participation whatsoever by the mother.

This theory was first proposed in this post on the imdb forum (not mine), which has a more complete explanation and more detail (and objections to the theory).
 * Alternatively, their mother absolutely loathes Marshall, Lily, Robin, and Barney, and can't stand talking about them. That's why she's not there, and the story of why she hates them so much will provide some drama for the final season.
 * Actually, Ted going to such depths in the story is from back in Season 2, he told his parents that when he had kids, he would tell them every detail of the story of how he met... well, you know. Ted's mom and dad couldn't go into deep personal discussions, remember, and it seems Future Ted has done a good job of not turning out the same.
 * Unlikely. The Front Porch shows that Ted is not going marry, or even date, a girl who hates his friends.

Future!Ted is no longer married to the mother
He's telling the kids the story to get them on his side, and the show ends with Future Ted (now Present!Ted) making an earnest effort to win her back.
 * Very, very plausible.

The kids are blind.
Future!Ted describes a painting to them...a painting that's hanging in their house. He doesn't say it in the same "as you know" tone that he uses for the toy bus, which they've presumably played with. This explains why the kids tend to stare kind of vacantly in the flash-forwards, and a little bit why Ted is rambling on so much: he was told that parents need to talk to blind children a lot, and is oblivious to the fact that they've grown up now and are perfectly capable of seeking out their own stimulation. Wildly guessing further: since both of them are blind, it's genetic, meaning quite possibly the Mother has very poor eyesight herself...she can see things close up, and she's very good at recognizing the color yellow, but she won't recognize Ted from his Econ lecture when next they meet.
 * Jossed as of Say Cheese. Future!Ted says the kids have seen Lily's photo albums.
 * Jossed two seasons earlier, with Season 3's Little Boys. We are shown pictures the children drew of themselves with Aunt Robin, something they couldn't have pulled off nearly as well if they were blind.

Ted's wife can't get pregnant.
Robin will give birth to Ted and his wife's baby. The story is still about how Ted met his wife, but the pilot episode turns out to really be about how Ted met the kid's birth mother.
 * ... surprisingly Jossed by "Symphony of Illumination."

The time in which Ted is telling his children this story is After the End
There was an apocalypse of some sorts, and Ted is telling this story to pass the time in their atomic bomb shelter. When in the beginning of season two, his daughter say it feels like he's been going on for a year, SHE MEANS IT. She's just not sure because they don't know the exact date. Is there any other real sign for this in the series? One time, Marshall says about the organization he idolizes and wants to join that they are going to fix the environmental issues. Future Ted comments "Well, at least they tried." Note that it couldn't have gone wrong long before 2030, since the kids apparently have been shown Ted's first building while going through New York (or this means that it's just not an Everything Trying to Kill You or everything is radioactive kind of apocalypse).
 * The room the story is being told in is revealed to be the living room of the house Ted bought in Season 5 and restored sometime in the future.

Future Ted is smashed.
Consider the facts: Ted is telling a very long, digressive, inconsistent and generally inappropriate story to his children, which doubles as a nostalgic look back at his single years. In his story, Young Ted and friends are almost constantly drinking, and apparently visit the bar every single night through a period of their lives which lasts over five years. Neither of his children seem particularly surprised by Ted's occasionally-scandalous actions in the story, or by the fact that their father is telling them this rambling, sometimes-sexually-explicit tale in the first place -- they're just bored and annoyed and want to leave but aren't allowed to. Also, Ted is best friends with Marshall, and who is canonically an extraordinary lawyer.

Conclusion? The Ted who is narrating had quite a few drinks before starting this story, which is why he's having trouble keeping track of the details, and also why he keeps forgetting that some of this material is not stuff a parent would usually tell their kids. When the kids protest that they've heard this story before, they're telling truth, as this is not an entirely uncommon occurrence in the Mosby household. The mother is not around because Ted is an alcoholic. Ted retained custody of the kids only because he has access to very good legal representation.
 * Or because he's not an alcoholic. He just gets kinda drunk at least once a week.

Ted is very unreliable narrator.
None of the people exist. The narrator is a psychotic man hallucinating the kids and his former friends. He's made up a perfect couple (Lily & Marshall), a stereotypic womanizing friend with a heart of gold(Barney). And a girlfriend who is beautiful, but represents the side of him that never wanted to commit.

Aunt Robin is, in fact, the kids's actual aunt
It's not a term of endearment. Ted, try as he might, is still longing for Robin when her now college age sister Katie enrolls in (his class). One night she and Robin are at the bar, Ted comes in while Robin's in the bathroom and strikes up a conversation, and...well...the rest (as they say) is history.
 * By extension, this means (at least) one of the other Honorary Uncle titles could be legit.

This is the first time the kids have been told anything about Ted's life before they were born
The story starts in 2005, but in the first episode the kids are confused that Ted just told them to story of how he met Robin rather than the mother. If they knew when their parents were married and how long they dated, they'd be able to work out what year they got together and so could just tell Ted to skip to then. It would also explain why Ted is making the story so long, he feels guilty about not telling them anything and so wants to correct it whether they like it or not.

Future!Ted's kids are named Luke and Leia
Ted is a big Star Wars fan (Marshall: "Ted loves Star Wars. He watches it in sickness and in health, in good times and bad, etc...), and when told to "swear on his unborn kids", he says "I swear on Luke and Leia". Given how Ted's ideal woman is practically him, the mother would probably be fine with naming the kids Luke and Leia.

Future Ted has Alzheimer's
Which is why he forgets old girlfriend's names, and why he ends up telling his kids about the time Barney had a 'Perfect Week'. Future Ted went to the doctor's, and found out he had the disease, so he decides to tell the kids about how he met their mother while he still can. Also explains why he's taking so long to tell the story, because he's forgotten how it happened, and is stalling for time until he remembers it. Could also be why he only refers to the kids as 'kids', because he doesn't remember their names.

Occasionally, the mother is in the room as Future Ted tells the story.
Future Ted seems rather inconsistent in how much he wants to censor for his kids. When the mother is nearby, he's a little more conservative than when she's out of the room.

Future!Ted talking to his kids isn't actually real; it's an Imagine Spot of Present!Ted in the series finale.
Ted is just imagining what his kids will be like and the story he will tell them. This opens up the possibility that anyone he said was not the mother could actually be the mother, even Robin; he just thought that they weren't at the time of the Imagine Spot.
 * Continuing with this theory, there could not even be a mother: Ted never ends up getting married and having kids.

Ted is actually Madonna
It makes so much sense! Both have slept with more people than they might admit, and both

Robin would eventually let go of her feelings for Barney and hook up with that guy in Hopeless.
...and then Barney realized that he still loves Robin.

The woman Barney is marrying is
Think about it. When Barney first meets her, she plays him like a violin, leading to him not being able to think about anything but her. This totally proves that she can keep up with him, at least in terms of magnificent bastardry. Not to mention, at the end of 'The Broath', there is the exchange with Barney asking [[spoiler: what would cause her to give up her job as a stripper, and Quinn replying with 'when she gets married'.

Barney doesn't marry Robin
I know. It's sad. I was hoping otherwise. But Robin would definitely have Lily as her maid of honour, right? So, as much of The Ladette Robin is, she'd probably have an enormously stressful wedding day and Lily wouldn't be running around informing Ted that the groom needed him. Also, since when is it like Robin and Barney to get married traditionally, in a church and all that?
 * The bride needed Ted, i think it's a very big hint that Robin is the bride, why would Nora wants to see Ted before her wedding? After all they (so far) barely ever talked with each other, heck did they ever talk with each other? So unless Nora and Ted formed a friendship with each other before the wedding, i think Robin has the bigger chance to be Barney's bride.
 * And Robin also asked Ted to be her best man if she ever got married. So Ted's probably pulling double duty.
 * If it's not Robin, I think it's Victoria. Why else would they bring her back?
 * To provide closure for her character?

Barney marries Robin.
From what we've seen in the final episode of season 6, Barney finally decided to enter a steady relationship with Nora. Robin on the other hand seems saddened by this fact. My take on this: Barney's relationship with Nora ends badly, Robin is there for him when the time comes, they get together again and decide to get married. Hence uncle Barney and aunt Robin.
 * Ted's nervousness at the wedding is also good support for this; if one of his best friends is marrying his ex-girlfriend, he'd be rightly nervous. If Barney is just marrying Nora or some other girl, it seems more far-fetched. Future Ted hasn't yet said Nora's name, however, so it's unclear whether she's "Aunt Nora" or "that girl Nora".

Barney marries Natalya from "The Limo"
This ties into the "Barney moves out of the country" theory. Natalya comes back into his life and the two fall in love. They get married, but after a few years, Natalya has to go back to her home country, and Barney ultimately decides to go with her.

Barney is bisexual.
And in love with Ted. Subconsciously, he doesn't want to admit his feelings for Ted, and so he urges Ted not to pursue long-term relationships, or any relationships at all. Similarly, his own philandering comes from his desire not to commit to anyone who isn't Ted. He and Barney get married (in the future, when gay marriage is legalized), or not (have Ted and the kids' mom ever been confirmed as being married?), and the kids' biological mother is Robin.
 * Or Lily. Or even a random woman who gave her eggs to the fertility clinic. But this theory is partly Jossed because Barney is against long-term relationships in general, he's also extremely happy when Marshall is single again, and is devastated when his brother gets into a long-term relationship and even married.
 * Barney happy when Marshall is single again? Do you even watch the show? Barney is the frickin' president of the Marshall/Lily fanclub.
 * And yet, it is rumored that
 * Barney and Ted eventually get together, get married/civil partnership'd, and decide to have kids. When they finally meet the perfect surrogate who has all the traits Ted wants his children to have and will play the right music for the fetus... it's Cindy's roommate!
 * Ted is definitely married as of the year 2021 -- in "How I Met Everyone Else", he wonders where his wife has got to, and in "Garbage Island" he tells Wendy he's married to a "wonderful woman" and has two kids.
 * Barney and Ted eventually get together, get married/civil partnership'd, and decide to have kids. When they finally meet the perfect surrogate who has all the traits Ted wants his children to have and will play the right music for the fetus... it's Cindy's roommate!
 * Ted is definitely married as of the year 2021 -- in "How I Met Everyone Else", he wonders where his wife has got to, and in "Garbage Island" he tells Wendy he's married to a "wonderful woman" and has two kids.

Robin ends up with Don.

 * Or at least, the writers planned it this way before the audience hated him. When Future!Ted originally mentions Don, it was that "ironically," after choosing to forgo dating for her career, that was the day she met him, and he says his first name with no other explanation, as if the kids should know already.
 * If Robin does end up with Don, why doesn't he refer to him as "Uncle Don", like he does with Lily, Marshall, Barney and Robin?
 * Wow, serious Fridge Brilliance. The irony in their meeting at their time isn't because she wound up with Don, but because in the end she was faced with the same choice, and chose dating... and he chose the opposite.

Don was either an Aborted Arc or will lead Robin to actually try to settle down in a long-term relationship.
His introduction by Future!Ted bestowed on him much more importance than the maybe-half-a-season relationship he turned out to be. Either Don was originally intended by the writers to last much longer than he did (as in, he'd still be around in 2030 as Uncle Don to Ted's kids), or Robin's finally realized she's willing to find a life-long partner and maybe husband. Granted, they broke up last season and there hasn't been that much follow through besides Robin getting emotional a couple of times, but if they bring back the concept, 2030's Aunt Robin and Uncle Mr. Robin will be a direct result of the Don relationship. Alternate theory: Don comes back, begs to get back together, and everything works out.

The wedding Ted is at in the first episode of the sixth season.

 * Almost certainly true.
 * Perhaps further support for this, or at least part of it:
 * Another popular guess is, since why else would the mother be at the wedding? Furthermore, Ted is nervous about his speech because he doesn't know the couple that well, but  insisted he be the best men because Ted played a vital role in her.
 * Maybe not, if this (confirmed here to be about HIMYM) is anything to go by. Possible spoilers.
 * And now, in episode 6.12 ("False Positive"), asked Ted to be her Best Man if she ever gets married.
 * My personal theory is that it's Barney's wedding. The woman who calls for the best man never says a name, and Ted and Marshall get up at the same time. And it would be just like Barney to ask them both to be his best man. Alternatively, if it turns out that this is Robin and Barney's wedding, then Ted is Robin's "best man" (as per "False Positive") and Marshall is Barney's.
 * This doesn't really prove anything, but in the latest episode ("The Exploding Meatball Sub") it shows a flashforward to 2021 at the very end.
 * Doubtful, since she's never referred to as "Aunt Nora" in the voiceover. And
 * Doubtful, since she's never referred to as "Aunt Nora" in the voiceover. And

Barney and Robin's marriage will not last.

 * In the Exploding meatball sub, ten years later, neither is wearing a wedding ring.
 * It is possible the writers did that because that was before it was revealed whose wedding it was and they didn't want to give anything away. It's possible though, as NPH hides his hand in 2015 so we can't see if Barney is still married or not. Considering the fact that the wedding is important in the show's story, however, and that Barney and Robin are still on talking terms in 2030 (it would be even harder for them to remain friends if they split up this time round), well, those are good arguments for them still being married. I also can't imagine why the writers would go to such lengths to make both reveals so big and important if they're only going to divorce the characters later.

Harold and Kumar takes place a few years prior to How I Met Your Mother
Although briefly reuniting at Christmas in 2006, Harold and Kumar's constant fighting eventually broke the pair up again. Kumar did, however, get his life together. He went into medical school, but his constant smoking prevented him from becoming a doctor, so he ended up taking psychology and becoming a therapist instead. Angry at himself for allowing marijuana to yet again interfere in his life, angry at his girlfriend for enabling him, he finally quit, left her, moved to New York, and changed his name to Kevin. Harold, meanwhile, without the calming influence of Kumar on his life, gradually got more and more jaded and cynical by working in corporate America. He, too, changed his name, not because he was ashamed of it, but because Jeff Coatsworth was a more effective name for Wall Street than Harold Lee.
 * Additionally, "Neil Patrick Harris", as seen in the film was in fact Barney using their similar appearance in one of his schemes. This would cover the fact that Neil Patrick Harris is gay and the man Harold and Kumar met clearly wasn't.

The whole show is actually a simulation showing a Five-player Tabletop RPG with each player filling one of the Five RPG archtypes
The telepathic conversations are how the simulation represents talking is a free action, the relationship arc between barney and robin was an attempt by both players to farm roleplaying XP, occasional continuity slip-ups such as the goat are the result of either the DM getting his notes mixed up or ted's player misremembering the events.
 * Robin's player is the Real man. She views the game as a straightforward attempt to amass as much money and status as possible and is confused whenever role-playing and character development/relationships. As a result her character has a poorly developed bakstory.
 * Ted's player is the Thespian. He's determined to roleplay a lovesick romantic but his poor character optimization and unwillingness to think strategically doom him to failure.
 * Marshall's player is the Loony. He ignored the game's romantice premise in order to focus on roleplaying a lawyer leading to many career oriented subplots. He also randomly introduces odd quirks such as singing everything and his love of girly drinks just for lulz.
 * Lily's player is the brain. Determined to advanced the plot and skilled at manipulating the other players to keep them on the rails.
 * Barney's player is the Munchkin. His character is optimized for getting laid as much as possible. He took the flaws: parental abandonment, fear of commitment, compulsively wears suits, unable to drive and does not know how to use screwdrivers in order to get money, corporate connections and a super-high seduction skill. He also designed his apartment to give himself as many circumstance bonuses as possible. The laser tag obsession is how he justifies it to the DM when he reflexively puts points into his combat skills. Barney's butt monkey status is the DM getting revenge.

How I Met Your Mother is an Alternate Universe of Friends.

 * Marshall = Chandler
 * Lily = Monica
 * Barney = Joey
 * Robin = Pheobe
 * Ted = Ross
 * The show is about finding Rachel.
 * Except that Barney is not stupid... and in what universe is Robin anything like Phoebe?
 * They're both the wacky chick (fulfilling similar roles in the group dynamic), and both have UST with their universe's Handsome Lech (although in HIMYM, it just becomes ST).
 * It's a very, VERY alternate universe.
 * Robin is much more like Rachel, and based on all the quirks Ted describes about the mother in "Girls vs. Suits", she'll probably be the Phoebe herself. Still kind of works, since Joey-Rachel and Ross-Phoebe were couplings that Friends experimented with.
 * I would gush if Ted met a "Phoebe" :D
 * How about an Alternate Universe of Coupling?
 * Marshall = Steve
 * Lily = Susan
 * Barney = Patrick
 * Ted = Jeff
 * Robin = Sally
 * Ted's various girlfriends collectively = Jane
 * I'd rather say Robin is Jane.
 * Not much point when Coupling is basically an alternate-universe Friends
 * Coupling is Friends if the four of the friends are retarded or insane.

How I Met Your Mother is an Alternate Universe of Scrubs.

 * Ted = J.D.
 * Marshall = Turk
 * Lily = Carla
 * Robin = Kim
 * Barney = The Todd
 * Perhaps the mother will be Elliot?
 * But, I thought that Elliot

Barney before his disillusionment was Billy, of Doctor Horrible's Sing-Along Blog.
Both characters begin as well-intentioned but timid, have something go very wrong with a girl, and in response seal up their hearts and become soulless bastards... though Barney's is played for laughs. Barney could be Doctor Horrible's civilian persona. (Admit it: it's creepily possible.)
 * Dude, Barney was a hippie, and Billy's a Deadpan Snarker. Huge difference.
 * But not mutually exclusive...
 * Billy's not a nice person. He mocks people's e-mails, is an aspiring super-villain, a stalker, and ponders mass poisoning simply because he got his heartstrings a little bruised. He already had one foot in the soulless bastard door when Act I started.
 * Disillusionment? Er, no, Barney's awesome
 * Plus, the Mega Corp that Barney works at is the perfect front for a legion-of-doom type organization
 * Also what is Barney's actual profession? I makes sense.
 * After his Heroic BSOD in Doctor Horrible, Billy accepted Bad Horse's offer to head up the Evil League of Evil's New York office (operating in the guise of a midlevel executive at the League's front company, Goliath Bank). Changing his name for security reasons, and desperate to fill the void left by the death of the only woman he ever loved, he begins a meaningless string of hookups, booty calls, and one-night stands. Meanwhile, Moist, with his share of the take from the bank heist, gets hormone therapy to treat his excessive sweating, earns a Master's in Engineering from M.I.T., and takes a position at Cal Tech, all under his real name of Howard Wolowitz.
 * Alternately, Barney is a more successful Billy in an alternate universe.

Barney's real father is John Constantine of Hellblazer fame
Take a moment and think about it. This is the Constantine of the comics, BTW. They both are blond and blue-eyed with the same overall build. John is wearing a suit underneath that trench coat. Plus, John's age (55) makes him old enough to have fathered 32-year-old Barney. Considering all the times his mom left him alone, it's not unlikely that she darted off to England to have a one-night stand with a certain bisexual con-artist magician. For all we know, Barney's pyrotechnics are extensions of his own magic powers inherited from Daddy Constantine. And then there's the bus accident from the season three finale. Barney survived with several broken bones and yet didn't wind up crippled. Obviously, he can ride Synchronicity Highway just as well as John can, by siphoning off the good luck of others.
 * His father in the show is to be played by John Lithgow

The mother has nothing to do with Ted's quest to get married
Ted gets around a fair bit, all things considered. He's no Barney, but he's bedded his fair share of ladies. Flash forward to the series finale; the episode is nearing completion with no mother. All of a sudden, a one-off love interest Ted knocked boots with in a previous episode walks in with a child in tow. Ted's child. Ted mans up and marries her.
 * Though, depending on how long the show runs, they will have been born after the show ended.
 * If the mother is planning on having Ted know about and be involved with his child (even willing to marry him because of it) then why would she wait until it's already born to tell him about it? Wouldn't it make more sense to contact him while still pregnant?

Altrucell, the company Barney and Marshall work for, is affiliated with Wolfram & Hart
Why? Come on, think about it:
 * Barney is a magician
 * Marshall is the biggest believer there is
 * Some of their employees are pretty weird
 * Barney is super secretive about his job and is afraid he'll end up being murdered because of it
 * If Barney is to be believed, then it isn't uncommon for armed and dangerous ninjas to show up at the office
 * They sure do some shady business around there...
 * Their security isn't that great - see "armed ninjas"
 * The company has been established as EVIL!
 * The Sasquatch at Barneys job in the first season wasn't Marshall, it was a real Sasquatch
 * Wolfram & Hart has offices in many dimensions and realities
 * And it would be cool

Also, it would explain the ridiculous number of Buffy the Vampire Slayer and Angel alumni on the show: because of the events of Not Fade Away, the Senior Partners had enough of Team Angel, and so they sent. To make sure the Scoobie Gang would stay out of it, they sent the rest of the characters in the Buffyverse into an alternate reality, erased their memories, and gave them completely different pasts, which is why Andrew is an employee at a coffee place and Willow is Lily.

Additionally, the Mayor is Ted's mom's boyfriend because, in this dimension, he never heard of demons and never died.
 * Because the Senior Partners were worried that the now memory-altered Scoobie Gang would run into their counterparts in the Motherverse reality, they killed those counterparts. However, they didn't need to kill Team Angel's counterparts because they are still in the Buffyverse . This is why Sandy and Penelope weren't killed; the original Wesley and the original Fred didn't cross over to the Motherverse.
 * Alternatively, they did not kill off the Scooby Gang counterparts. We know that Lily/Willow has a doppleganger, who is a stripper. Who's to say that the rest of the Scooby Gang doesn't have dopplegangers too, just ones that we don't meet?
 * Maybe Barney's job is to make sure that Lily doesn't remember that she is Willow.

Barney and Richard Castle actually made up Dr. Horrible's Sing-Along Blog together
In reality, Barney and Richard Castle are friends, if only by the Internet, and they came upon Felicia Day's web original The Guild and concocted a plan to write up a blog, since Barney loves blogging, that stars their alter-egos. Felicia Day agreed to it. So Barney and Castle wrote up and starred in the Sing-Along Blog as enemies. Also, Felicia Day is a doppelganger of the Slayer Vi, which, in coordination with the Wolfram & Hart theory above, connects the Blog to How I Met Your Mother to Buffy and Angel.
 * Alternately, rather than Felicia Day and Simon Helberg, in this universe Penny and Moist were played by Codex and Howard Wolowitz. Possibly the greatest crossover ever?

Marshall is a Time Lord, but he doesn't know it yet.
You knew this one had to come up eventually. Okay, so it's canon that Time Travel exists, or will exist in the future, in the Motherverse. And we even see Future!Marshall spying on Present!Marshall and Present!Lily in 2009. So obviously the only explanation is Marshall being a Time Lord. Why doesn't he know it yet, then? Probably he's under the same stuff the Master was in "Utopia" and it's just a matter of time until something brings back his memories.
 * Future!Marshall was wearing a bowtie. Gee, who do we know that travels in time while wearing a bowtie?
 * Alternately, assuming that the "Marshall becomes President" theory is true, and knowing he's a fan of Quantum Leap, perhaps he ordered the construction of a working time machine after a long marathon and volunteered himself to be the first person to take a leap.

How I Met Your Mother and the Buffyverse are in the same universe.
Think about it. How I Met Your Mother shares several actors with the Buffyverse. It was stated by another Troper that the company Barney works for is affiliated with Wolfram and Hart. The Motherverse seems to be a pretty fantastic world itself so it wouldn't be outside the realm of possibility that they would at least be in the same universe. Lily is actually Willow under a new identity. She eventually tired of the Scooby Gang and their antics and pretty much just wanted to be normal, so she cast a spell on Ted, Marshall, and Barney making them think she had been in the group all along. Sandy and Penelope are just doppelgangers for Wesley and Fred, but Andrew was undercover working in the coffee shop. Willow had put the spell on the Scooby Gang, erasing all memories of her, which is why Andrew didn't seem to recognize her, and Lily was more concerned about finding out what Chloe looked like, which is why she didn't seem to notice anything. This could also be why Lily's favorite name for a girl is "Tara" and why she seems a little bi...

Ted is some how related to the The Wonder Years family

 * Clearly a long, drawn out narrative recounting every incident of your life is In the Blood.

Barney or his employers will eventually reference "that genius kid who knows enough to recognize one of our agents but is stupid enough to blow up his elevator".
It's not a Chuck Lorre production, but it is in the same block, and Barney does something that involves North Koreans, lots of secrecy, and the occasional ninja assassin.

The company Barney works for is a front for COBRA
Think about it: what do we know about the company Barney works for? Sounds a lot like COBRA to me.
 * They spend a lot of time acquiring banks, and theoretically, have a lot of bankers/financiers working with them
 * They're evil
 * They regularly get attacked by ninjas
 * They have destabilized at least one nation
 * They regularly do business with countries the U.S. considers threats (North Korea and China, at least.)

Barney's father is the Trinity Killer.

 * He has a dark past, but has an overly perfect looking family with a son and a daughter, and even an estranged much older sibling from an earlier relationship.

Barney reads A Song of Ice and Fire.
That's how he came up with the "Don't poke the Dragon" line in "Garbage Island".
 * Alternatively, he reads Harry Potter. Hogwards' motto "Draco dormiens nunquam titillandus" also translates "The sleeping dragon must never be poked".
 * Titillandus has connotations of "tickle" far more than "poke", and is typically translated that way. There are also unrelated, nitpicky problems with the translation you chose. As for the original WMG, "don't poke the dragon!" or "don't poke a sleeping dragon!" has been around in certain wide-ranging, fantasy-fan circles for years before A Game Of Thrones was released, possibly as long as or longer than First Edition D&D has been around. That doesn't mean he didn't get it from A Song of Ice and Fire, and I'm pretty sure he does read the Harry Potter books, but my memory can't supply specific examples.

Barney's father is The Spy
The obsession with suits and his way with the ladies is clearly In the Blood. This may mean that GNB is a subsidiary of Team Fortress Industries.

Ted's sister is a time-traveling teenager with attitude from the year 3000
Thus, why she hasn't been seen outside one episode. Her team determined that Ted is not a match for Alex's DNA.

Zoey is .
Time inconsistencies aside, both share some traits and qualities (headstrong, blonde-haired, some others).

Future Ted is making the whole thing up as he goes along, based on objects in the room, a la The Usual Suspects
We know that things on the shelves are supposedly integral to the story. Perhaps instead of being things that are actually important, they're just random stuff on the shelf that Future Ted uses to flesh out his story.

The doppelgangers are the future selves of the main characters.
Moustache Marshall? Marshall with a moustache and accent. Stripper Lily? Lily with an accent, a corset, and a lot of practice with a stripper pole. Lesbian Robin? Someone convinces her that playing amateur baseball (America's national pastime) and being a hockey fan/being Canadian are not exclusive (they already won half the battle with that scene in the Tim Horton's), she gets gum in her hair and has to cut it short, they realize who the doppelgangers really are and Future Future Marshall shows up with his time machine.

Mad scientist Barney will be the fifth dopplganger.
Either all the doppleganger's are from Dr. Horrible's dimension or Dr. Horrible is Barney's Evil Twin.

Hippie Barney will be the fifth doppelganger.
When he was younger he wore suits, but then was disillusioned with the whole idea of corporation when he slept with his boss (which was probably but not necessarily female) and decided to become a champion for Earth. They will find him on a picket line for Wolfram and Hart Altrucell.
 * "Eventually, we all become our own doppelgangers...."
 * "Eventually, we all become our own doppelgangers...."

The fifth doppelganger will be Lily's substitute gynecologist.
And he will serendipitously tell her and Marshall that she's pregnant.

Barney's doppelganger will be played by Neil Patrick Harris...
...AsHimself.

They won't actually see Barney's doppelganger.
"Remember, kids, when I told you that we saw the rest of the doppelgangers that year? Well, I lied. Your Aunt Lily and Uncle Marshall thought they saw the fifth doppelganger, and they were looking forward to having a child so much that we all played along. Except for Barney, who wasn't there because he was busy walking past the bar window in a sombrero and knitted poncho. We did eventually see Barney's real doppelganger, but that is a story I'm not telling you until you're older."
 * This would probably be for the best, seeing as it would be very unrealistic for all the group's quests and traditions and such to end conveniently right before or when he meets the Mother.
 * This would probably be for the best, seeing as it would be very unrealistic for all the group's quests and traditions and such to end conveniently right before or when he meets the Mother.

Barney's doppelganger will be a Ninja Pirate Zombie Robot of characters played by NPH.
He will be an amateur musical actor from Ohio who is in New York to be in a play about an Ineffectual Sympathetic Mad Scientist. The gang meets him when he tries to pick up Robin with an incredibly cheesy pickup line about how he graduated from medical school before he was 16, then as he's leaving says he's going to go "pick up a cougar with my huge bag of catnip, if you know what I mean".

Barney's Doppelganger was in the episode.
It was NPH on a robot unicorn, but you can only see him after consuming 83 sandwiches. It was mystical.

Barney's doppelganger will be Doogie Howser, M.D.
This was sort of verified as the fertility doctor that Lily sees is Barney's doppelganger.

Unlike the other doppelgangers, Barney is actually related to his.
Dr. Stangel could every easily have the same father as Barney. I don't remember the last name given for Barney's father, but even if it was different, Dr. Stangel could also have been only raised by his mother without the father's influence.

The sixth doppelganger already appeared on the show
The Mother's doppelganger, who will be played by the same actress, had already appeared in a previous episode before. She might even had been a named character. This fact alone will instantly win her points with the rest of the group.
 * YES.
 * Or lose her points, depending on who she's a doppelganger of.

The rest of the Doppelgangers will return
Stripper Lilly was how we where introduced to the doppelgangers

Lesbian Robin isnt a lesbian
She just has short hair and was playing softball, but she is the mother.

Barney's job is illegal
His company won't allow him to tell anyone what his job is because the job isn't supposed to exist (of course, it can't be too evil....)

Barney is a prostitute.
Whenever he is asked what his job is, he answers "Please." ... He pleases people for a living.
 * Except we used to see him at work, we just didn't know what he actually did. And he hasn't said that since his company was bought out by GNB.
 * No, we saw him in an office. We never saw that office being used, since we never saw him do anything. For all we know, he was just a good enough prostitute to be able to request an office and a parking space for him to play out his fantasy of being a high-flying executive.
 * Or he could be a private prostitute for GNB employees.

Barney is a mathematician.
He is a high-functioning autistic savant, who is ridiculously good with numbers (he could memorize a metric shitton of prices and add them up for The Price Is Right). His job at the company is finding ways to evade taxes, that's why he can't discuss it.
 * Autistic? He's been mentioned as having ADD, but that's it.
 * I don't know, he was able to memorize the names of ALL of Ted's students....
 * I don't know about the rest, but "evading taxes" makes sense. There's those shadowy deals he seems to make with North Koreans, and in one episode Barney tells Lily about a secret locked case in his apartment. If he ever dies, she's to take it and burn the contents. Hmm...

Barney's job is much more benign than he makes it seem.

 * Throughout the run of the show, we're shown that Barney's a MUCH less evil guy than he builds himself up as. His job is likely something very beneficial, likely involving ethics or something similar, but for the sake of his "bad boy" image, he refuses to disclose the details to make himself seem more of an "evil exec".

Barney will lose his job soon.

 * Because him giving up on romatic relationships and his father just isn't enough.

Barney doesn't know what he does
I forget my reasoning but something to do with the episode Doppelgangers
 * Barney said something to the effect of "They actually expect me to work"

Barney is President of GNB.
Altrucell is a gigantic conglomerate that seems to have its fingers in a lot of pies. When the company took over GNB in a hostile takeover, Barney was thrilled about it because the corporation was putting him in charge of their new GNB division. Barney appears to have near-limitless freedom at work and personally arranged for Marshall to get the job in GNB's legal department. Since GNB is now a subsidiary of Altrucell, Barney's position is pretty much just a title, an office, and a fat paycheck. People ask what his job is and he says "Please" because it would be easy for any of them to look it up on GNB's website.

Barney is a janitor at Goliath National Bank
He "has a lot of keys" according to Marshall. He has on occasion gone to great lengths to preserve his image, and always manages to sit in his office in a clean suit when his friends arrive.

Barney is a liar for hire
When he is directly asked, he responds with "Please...", almost as if he was asking to drop the subject. If in the past he had spoken with his friends about his strict need not to talk about his job under any circumstances, "Please..." becomes short for "Please, we've been through this. You and I both know that I can't say anything else." He knows all the company secrets: "The things I know about this company, I can never be fired. My body might wash ashore with no fingerprints or teeth, but I can never be fired." He once insisted: "If I'm a terrible liar, then why am I not in prison for perjury? But I don't want to talk about work." Suppose Barney is a professional courtroom liar. Any time the company is involved in court proceedings, Barney is given appropriate fake credentials and temporarily given a job description that makes him a fitting witness for the company. He adopts new personalities for the duration of the court case, lies about the company's culpability and explains away all the evidence against them. From this point of view, his womanizing outside work draws on the same talent pool: wild theories to persuade the gullible, new personalities, explanations for everything, and of course the willingness to throw ridiculous amounts of money at problems. As a professional liar, Barney is privy to all of the real evidence against the company and they pay him a lot because his testimony is substantially cheaper than paying off all the lawsuits.

The fifth slap will set off a chain of reactions that leads Ted to the mother.

 * Jossed, the fifth AND sixth slaps happened
 * lets say the last slap

Marshall has already used the 5th Slap.
In Girls vs. Suits Marshall slaps Barney after he starts fondling Marshall's suit. Barney will bring this up when Marshall tries to slap him again, pointing out that he has already slapped him previously to this. Barney will declare that Marshall has been...Lawyered.
 * It's not Barney's call what counts as a slap, it's Lily's. If Marshall didn't slap him in the face as hard as he could, it's not one of "the slaps."

Robin actually was in a porno.
At no point has Robin actually explicitly denied being in a porno. Barney will discover this at some point and unleash the most legendary slap ever on Marshall...only to find out it was softcore.
 * If this happens I hope it's an in the future gag.
 * Maybe 'Teenage Pop Star' is Future Ted's Euphemism for 'Teenage Porn Star', similar to how 'sandwich' is his word for marijuana.

Barney has a heart condition, which will be what kills him in the future
I'm going along with the WMG that says Barney is dead by the time Ted is telling his kids the story. In 'A change of heart', Barney goes to see a cardiologist who (unlike she did with Ted, Marshall, Lily, or Robin) makes Barney wear a heart monitor. Sometime this season, the cardiologist will reveal that Barney has a heart condition and can no longer maintain his wild lifestyle, possibly forcing him to settle down.
 * A sudden, sharp shock to the face could perhaps send him into ventricular fibrillation. A sudden, sharp shock such as the final sla- No. It's too depressing. Barney will live forever, and if he doesn't, it will have nothing to do with Marshall.

The last slap will happen in the final episode.

 * Because honestly, if the last words of the show aren't "AND THAT'S FIVE!", I'll eat my hat.
 * The fifth slap happened in season 7 but Barney agreed to three more slaps in exchange for not wearing the ducky tie. Slaps 5 and 6 happened one after another but Marshall now has slaps 7 and 8 still available
 * How about "AND THAT'S EIGHT" instead

There will be a total of 10 slaps
8 is just a random number

Barney trades back the extra slaps in exchange for putting on the ducky tie again.

 * In a flashforward set in a casino where Marshall goes into Beercules-mode again, Barney is seen wearing the ducky tie again. Therefore, we know that sometime in the future, Barney will have to wear the ducky tie again...and it's unlikely he would accept wearing the ducky tie as part of a completely new bet, since it bit him in the ass the last time.

Eventually the total number of slaps will be 83.

 * Over the course of years, more slaps will be added as Marshall earns more. Since 83 is Barney's favorite number, it will ironically be the total number of slaps.

Barney gets retribution and earns a chance to slap Marshall back.

 * Eventually, Barney will employ a great usage of Insane Troll Logic to get back at Marshall (and Lily, since this troper believes her to be a biased Slap Bet commissioner). Lily is forced to accept Barney's logic and will have to give out a bigger punishment to Marshall.

Stinson Missile Crisis is a parody episode
every unrealistic or overdone aspect of the show is either commissioner or exaggerated in this episode. the A-plot exagerates how Robin gets when she's jealous by having her drinking under her desk. improbable coincidences are exagerated by Ted doing the same. the A-plot also exagerates Barney's womanising with schemes that are beyond ridiculous and almost impossible to believe (even moreso than they've ever been before) meanwhile the B-plot has Ted acting obliviously weird and it's pointed out that he could really benefit from therapy. Lily does something out of character by even considering drinking while pregnant just so her, Marshall, and Ted could have a storyline which involves her and Marshall having yet another disagreement about how to raise their child. towards the end, Ted explains his behaviour with the fact that he STILL hasn't found the girl of his dreams and his family life is so far away and is imediatly reassured he'll find her because that has to happen about once an episode. and the icing on this parody cake is that Robin is telling the story this time and just as Ted is doing to his unfortunate children and us, she keeps talking about what Marshall and Lily are doing and insists that it's important to the story only for us to find out in the end that it really isn't. when Ted tells her about the cheesy aesop of the week, she gives the unnatural reaction of explaining that his story will be intregal when she later tells her story (as if she knew at the time that she would tell it) which indicates that all the other times in the show when characters say simmilar things, Future Ted is probably making it up. and her therapist knows she made that bit up just like we know Ted made up "and we really chanted" conclusion: the Robin in therapy framing device was a way for the writers to show self-awareness and mock the way the whole series is being presented and mock aspects of the characters (it's perfect because the character's deviations from their normal selves can be explained by it being a different narrator)
 * I agree. Also, Lily and Marshall accuse Ted of invading their personal space in college, when really both of their first times (the real one and their first one as a married couple) were them deliberately ignoring that Ted was there, and Ted didn't enjoy being there. At first I was angry that they'd seemingly forgotten this detail, but it makes sense if you think about how Robin was the one who was narrating; she probably didn't know the details, and seeing as she sees Ted as being rather nosy, this was probably her assumption when she'd heard about Lily and Marshall's college experiences.

Ted is bad with numbers. This will eventually become a plot point.
Let us first state the obvious: This show knows how to handle subtle hints. Take for instance "single stamina", from which we can learn that Ted and Robin will break up before the wedding of James Stinson.

Now, let's look at two little things shown to us in The first season:
 * In machmaker, Ted finds out that his 9.6 match has been already set up with a 8.5 match. He says "she can do 11,45% better", and even proudly proclaims "That's right: I did the math". Ted, Ted, Ted... The other match is (1.1/9.6)*100% = 11,458333% worse than you, but you are (1.1/8.5)*100% = 12.941176% better than him. Writers Cannot Do Math, or clue?
 * When Ted is dating Victoria, He is waiting for a phonecall at 11 pm. While there is a six-hour time difference between Germany and New York, Germany is six hours ahead - It's 5 AM there, not 5 pm. This mistake leads indirectly to their break-up - if Ted had known this, he would perhaps have been more patient. Hollywood Science, Writers Cannot Do Math, or clue?

Now, let's put them together... Ted has made two mistakes using numbers. Twice has the mistake been so subtle, that the mistake has yet to appear on any tv goofs site (save for the time zone, which gets mentioned at tvtropes in Hollywood Science). Twice has it been roughly the same mistake - he has the correct numbers but mixes something up - in both mistakes he calculates the wrong way around.

The theory is thus: Towards (or even in) the last episode, Ted wil make some vital number-based mistake that will prove vital to him meeting his future wife.

Ted Mosby is really a jerk.

 * Okay, first of all, it's firmly established that Ted is an unreliable narrator. But can't that go a lot further than just forgetting details and making some of the stories more kid-friendly? What if he's telling the story to his kids to put a much better spin on things, rather than letting them find out from other people? For example, The Wedding Bride movie gives a pretty awful account of Ted and Stella's relationship, and if there's a worldwide film about it, Ted probably wants to make sure his kids don't think that's how he really is. But maybe he really is a jerk. He breaks up with a girl on her birthday (Twice!), fires Hammond Druthers in a pretty awful fashion, can be a major snob, doesn't give a toast at his mother's wedding, calls Lily a "Grinch", lies to Robin about Victoria, treats women pretty badly when going along with Barney's schemes, et cetera et cetera. Maybe he really is a jerk, and he's lying about it so his kids will like him (Because it doesn't look like they have a whole lot of respect for him anyway).
 * Lily really was a grinch, Hammond deserved to be fired, and his stepdad was singing a song at the reception about how he gets a massive boner when he fondles Ted's mom, so it's quite understandable that Ted didn't want to give a toast.
 * ..All of which we hear from Ted's perspective. Why wouldn't he change the details to make himself look better?
 * His story also contains tangential, all-too-convenient explanations of why there's a "Ted Mosby is a jerk" website, and why there are pornographic films about Ted Mosby -- both stories relying on two different people appropriating the identity of "Ted Mosby, Architect" for their own unsavory purposes. What are the odds of that?
 * Alright, but in the case of the porn films, if he were the Ted Mosby in question, why would he draw attention to the films at all? Wouldn't it be smarter to play the odds that the kids would never stumble upon the films accidentally rather than giving them a reason to google it?
 * Lily was a "grinch," and many people would have called her the same. This troper is more surprised that Barney, at least if not also Robin, called him out on it. Lily didn't just break off the wedding, but also cut off all communication with everyone - Marshall, Ted, Robin, and Barney. Not only was Ted friends with Lily as long as Marshall, Lily entrusted him with the secret of the try-out with the promise that she wasn't going to go.
 * I think you may be onto something here.
 * Wait, how does sleeping with random people make someone a Jerk?
 * Don't forget the way he presents a win-win compromise to Zoey, and then immediately trashes the plan the moment he learns that she's married. Dick move, dude.
 * At least twice he has dumped a woman with words to the effect of "Yeah, you gots to go."

Ted Mosby in fact far nicer and doesn't give himself credit.
Remember how ted warns Robin's younger sister about amorous boys by telling her he's was a horndog teenager who deflowered his smitten girlfriend and bolted? When in fact it turns out reverse was in fact true. This suggests that Ted plays up his youthful mistakes to serve as cautionary tales for his children. He's also is too soft to tell them what uncle Barney or aunt Lilly are really like and glosses over any consequences of their actions.

Of course he could of being telling the sister the truth and lying to Robin and his kids.

Ted will get fired next season for dating every girl in his class (or not stopping Barney from doing so).
That'll tack on at least three more years before we find out who she is. Alternately, he dates (or Barney sleeps with) every girl but one, and gets cut off every time he tries to say "except [future kids' mother's name]," since that would be the obvious giveaway.
 * Except, and both men haven't expressed any interest in dating Ted's students yet.
 * More importantly,

Lily is Bisexual
In "The Prom" she complains she never got to have her lesbian experience, in "Do I Know You?" she comments she won't pretend she hasn't noticed Robin's body, in "Double Date" she's a little too excited to meet Stripper!Lily, and in "Robin 101" Lily said Robin is the "occasional guest star in some confusing dreams that remind her a woman's sexuality is a moving target". Come on, the evidence is all there!
 * Single target bisexual? Her interest in men appears to be limited to Marshall, and her interest in women appears to be limited to Robin. Stripper-Lily is neither here nor there, since sexual attraction to one's self (which it essentially is) doesn't figure into the Kinsey scale.
 * Quick correction there- in "Old King Clancy," Lily says that if she could have sex with a celebrity, it'd be Hugh Jackman, so apparently she finds men other than Marshall attractive.
 * On the other hand, Hugh Jackman.
 * It would make sense, especially if the Buffy/Angel theory is right.
 * "Girls vs. Suits" more or less confirms this; Lily admits she was thinking of the hot new bartender (Stacy Kiebler) while having sex with Marshall.
 * And in "Hopeless" she is revealed to also have a crush on Mila Kunis.

The last "Present-time" words of the show will be, "Haaaaaaaaaave you met Ted?"
And that's how he meets their mother.
 * I fully support this being what happens.
 * Addendum: the actual courting will be a theatrical film.
 * So much support for this.

Ted Doesn't Remember How He Met Their Mother
Bear with me, because this only makes sense from an obsessive "I've watched every episode multiple times" perspective. Ted forgets/misremembers/misreports important details. He changes stories, characters, and events over the course of the show. It's probable that the writers just kind of gave up on some forms of consistency and continuity, but what if Ted honestly doesn't remember how he met their mother? It adds up: It's entirely possible that these changes are reflective of what the people actually did (Lily did change the explanation of why she painted a nude/Robin forgot the earlier explanation; Stuart divorced and remarried; Marshall pretended to have never been in a fight before; ect.) but it seems more likely that Ted is an unreliable narrator. Given this, we also have an explanation for the seemingly unending stream of filler episodes in the current season: he's buying time trying to remember.
 * Ted changes the physical characteristics of Stuart's wife (originally blond, tall, and somewhat plumper; later short, brunette, and petite)
 * Ted changes the explanation for why Lily painted a nude portrait of Marshall, and forgets that everyone in the group would have already known the story. The original explanation was that she needed to draw a nude portrait for class, and Marshall didn't want her seeing any other man naked. When it came up again in S 4 E 16 "Sorry, Bro", the rest of the group didn't know why Lily drew Marshall nude (despite being told in S 2 E 13 "Columns"), and Lily gave the explanation that "he ate my bowl of fruit".
 * This was the explanation for why she needed to do a nude painting at all. Maybe there was a list of assignments and she just chose the first one she saw, which was 'nude painting', after Marshall ate here original subject.
 * There is literally no time between the end of season 2 and the beginning of season 3 (the former ending on "it's going to be legen-", the latter starting on "dary, legendary"). How is it, then, that Barney could "already have a girl from work lined up" for Ted?"
 * Because IT HAPPENS THAT FAST.
 * Keep in mind, Barney would never intentionally set Ted up in a legitimate relationship. To Barney, having a "girl lined up" means "I just this second thought of a totally hot chick that you I could bang."
 * Marshall changes from having never gotten in a fight before, and not really knowing how (S 1 E 3 "Sweet Taste of Liberty", S 1 E 18 "Nothing Good Happens After 2 A.M") to being a skilled/crazy fighter with a background of violent fights with his older brothers (S 4 E 10 "The Fight").
 * He could have just never fought another person before - most people don't really count sibling fights as 'real' fights.
 * This last one is arguable, but Barney's reason for sleeping with so many women is also changed over the course of the series. Originally, it comes as a result of losing his girlfriend to a guy in a suit, and becoming cynical and disenchanted (S 1 E 15 "Game Night"). This later becomes because in middle school, a bully claimed to have slept with 100 women, which inspired Barney to sleep with 200 (S 4 E 22 "Right Place, Right Time")
 * He started his mission of sleeping with 200 women, met the girl of his dreams, lost her to a guy in a suit and decides to continue his plan.
 * Really? It is still possible that the story really is that convoluted. Don't forget, it's been established that Robin is essential to meeting the mother, which is why it's gone on for so long- Ted has to start from when he met her and go through each individual segment for it to make sense. Also, you seem to be forgetting a very important detail of Ted telling the story to his kids: he told his parents that, when he had kids, he was going to tell them the full story, bar nothing. He's living up to that promise, but he's just getting distracted sometimes with certain side-anecdotes and forgetting details. And some of those inconsistencies can still make sense: Stuart's wife could've had the same name of another of Ted's friends, and he confused the two temporarily after years without contact, we know Marshall is adverse to physical violence so very plausibly could hide that part of his past, and so on and so forth. Plus, is it really plausible that someone who is as big of a romantic as Ted, whose entire motive is finding his own true love story, would actually forget how it turned out?
 * And it seems that this is well and truly disproved as of "Girls vs. Suits."
 * Stuart's wife is played by Virgina Williams in "Intervention" as well as "The Wedding" and "Drumroll Please". She just changed her hair.

Cindy wasn't entirely honest with Ted.
Specifically, about not being able to date him. According to a certain other wiki, it's not against policy for students and professors to date at Columbia (the university Ted works for). Now, the question is, why would she have lied to him? Well, we know that  So the most obvious answer would be
 * Half-Jossed.

== The last episode of the series will contain something from every single episode related to Ted's journey as a character, allowing him one single moment of perfect clarity, where He Meets Their Mother ==

I dunno, just with how Continuity Crazy the writers are, it seems like something they'd do. It'd be a great way to tie the series together as well, meaning that every single step had a purpose, even some of the non sequitur episodes/moments.
 * Possibly in the form of a more convoluted version of "Right Place Right Time" (season 4) combined with a Clip Show.

Barney has, or believes he has, a very small penis.

 * He makes up stories about how he has a huge one in order to impress women because he's convinced that his is too small.
 * I have visual proof that if he thinks that he's very much mistaken. Er, I mean, I was taking screencaps and posted a picspam of season 5 episode twentyone, someone on my livejournal told me to take a closer look at Barney's trousers in this screencap
 * Of course Barney would own Bigger Is Better In Bed

The Wedding Bride was, for several cumulative reasons, not as divorced from "reality" as the show would have viewers believe.
Ted gave a story slightly biased towards himself from what he saw after twenty years of The Fog of Ages and twenty years to heal his spite towards Tony. Tony gave a story slightly biased towards himself from what he saw (which was less than what the viewers and kids saw), with a few twists to make it more marketable. Ted exaggerated how much of a Take That and Tony Propaganda-fest the film was after twenty years of The Fog of Ages and boycotting the film.

The Last Season
...will largely consist of Robin and/or Barney subtly mentioning here or there that they know the perfect girl for Ted. However, because Ted is already in a serious relationship he will say no to meeting her. Ted and his love interest break up, and in a particularly rough patch he agrees to see the girl. The series ends with him meeting the girl, who happens to be the mother. Bonus Points if the (almost) last line is some extent of "Have you met Ted?" to reference another theory on this page.

How I Met Your Mother will continue up to the birth of Ted's children.

 * Because, technically, they won't be their mother until after they're born.

Marshall and Lily have an abusive relationship.

 * ...and Ted is just naively blind to it because he believes in their love so deeply. In "Zoo or False", Lily mentions that Marshall has a habit of accidentally injuring her, but Ted was only present for one of the incidents she describes. In all the others, she and Marshall are alone. Marshall and Lily seem perfect for each other... impossibly perfect. Is it really so much of a stretch that sweet, sensitive, put-upon Marshall has a secret temper?
 * Well, that would make the fact he (very badly) didn't want her to get a gun much, much darker.

Marshall and Lily never have kids.

 * They were briefly having unprotected sex and Lily didn't get pregnant. Now, that's not proof of anything, but normally when characters are making plans/speculations from the future, Future!Ted comments or at least hints about what will happen. Future!Ted has NEVER mentioned Lily and Marshall's future children or commented on whether Lily will ever have any, and one would think from their relationship that children would be a foregone conclusion. Maybe they don't ever have kids at all.
 * There is a mention of it, in fact. In the smoking episode, future Ted mentions that Marshall had his last cigarette when his son was born.
 * He didn't say it was with Lily but...

Season five will be retconned. Heavily.

 * Many of the characters act wildly OOC and some of the stories are just ridiculous. This season was also the one that most heavily called the truth of the events into question, and was widely disliked by fans. The writers will probably take the opportunity to "smooth out" a few of the more despised details and get the show back on track by Future!Ted elaborating or admitting that he was exaggerating.
 * Alternatively, season five was All Just a Dream and season six will start with Future!Ted explaining why it was so important to tell his kids about some dream he had.
 * Not likely, though it's probably interesting to note creators and showrunners Carter Bays and Craig Thomas were missing most of the season to work on a Fox pilot that didn't get picked up.

The reason for all the inconsistencies is not Unreliable Narrator.
It's Time Travel.

Last Cigarette Ever provides a clear example of this: present!Marshall jumps back and beats the crap out of past!Marshall. Note that prior to this episode, none of the five smoked. It's precisely because present!Marshall did this that they all started smoking in the first place -- past!Marshall did so as rebellion against the random guy from the future. In addition, Marshall and Lily's love-at-first-sight bit was strengthened by past!Marshall's receiving that photograph.

The contradiction between The Fight and Sweet Taste of Liberty is resolved exactly the same way. Sweet Taste of Liberty is told before Marshall beats up his past!self, and thus he'd never been in a fight before. The Fight is told afterward -- present!Marshall's actions spurred past!Marshall's brothers into fighting.

The greatest Barney quote will be the greatest timeskip ever.
Okay, series finale, they're all in the bar. Baney is looking at some girl, as Ted and Marshall walk over to her. Barney is saying that Ted having sex would be legend- wait for it- as Marshall says "Haaaaaaaave you met Ted?" Cut to the Future year. Barney knocks open the door and goes -dary.

The characters were in fact eating sandwiches.
But they were cannabis sandwiches. Ted's shamefully tone implies that's regulate smoking as become even more looked down upon in the future. This caused pot head to turn to more sneaky way to get a fix. By 2030 or so Food Pills have become the normal thanks to environmental destruction (at least we tried) meaning that sandwiches as snacks have all but been forgotten.

Barney's father is Ted's future father-in-law.
Barney's quest to find his father is directly related to how Ted met the kids' mother, because Barney is the mother's long lost half-brother.
 * On another note, Barney has mentioned having a younger sister at one point, so it's quite possible that she might be Ted's future wife. If the wedding where Ted meets the mother is indeed Barney's wedding, then it's quite possible that Barney's sister will be there.

Don's depiction is just an example of Ted being an Unreliable Narrator (keep in mind I haven't watched season 5 just yet, so Joss me if you will)
He's actually an okay if rough around the edges guy. Ted just really, really doesn't like him but decides to be passive-aggressive about it by making him look like an asshole while still objectively presenting the group's reactions to him.
 * That sounds plausible considering Ted was probably angry at Don for breaking Robin's heart: he was the one who had to deal with her dealing with the break-up.

The series finale will end with the full version of "Hey Beautiful" playing.
Because why not.
 * Hey Beautiful will be playing when ted meets the mother (over a stereo or radio). To foreshadow this, there will be snippets of the song audible throughout the series where he meets the mother, signifying she is somewhere in the scene.

Barney's incident at the Natural History Museum didn't happen.
Just to be COMPLETELY EVIL. Barney hired the guard to drag him and Robin into the office and set up a "file" detailing the supposed Blue Whale incident. Then Barney added the whole "Uncle Jerry is my father" thing to the file in order to get Robin to fall in love with him again.
 * Jossed. The incident did happen and Jerry is indeed Barney's Father

The Wedding Bride was written by Tony.
But due to excessive Executive Meddling the story was completely changed around in order to make it more marketable.
 * I hope this is true, because that movie made me want to slap Stella and Tony.
 * This seems pretty plausible (after all, how many romantic comedies give nuance and complexity to the antagonist?). It still doesn't excuse them not giving Ted some kind of heads-up, though.

Ted wasn't that much of a jerk.
He is a pretty Unreliable Narrator, and undoubtedly exaggerated the personalities of a lot of the characters in the show. He clearly dislikes how he was when he was younger and wants to keep his kids from making the same mistakes, so he makes his stories as Anvilicious as possible.

Marshall's father wasn't worried about Marshall's fertility...
...because Future!Marshall has already told him that he can (and will) have children. Makes sense: Marshall will have access to time travel, it's proven. He and his father were very close. So on his first trip back to the past he will surely want to talk with him again.
 * If that is true, I hope it doesn't make it to air. It just seems wrong to mix what is one of the shows sillier aspects (and I want to make it clear that I think the silliness is good on this show) with their most serious story to date.

Ted's sister moved back to Ohio
After the episode where Ted co-signs her lease, she never appears or plays a part in any events in future episodes, despite working for GNB, the company Barney, Marshall and Ted are working for. Well, she never really "grew up". She and Barney DID have sex during the interview and just ran a con on Lily and Ted, and she got the job at GNB (Barney's hands were tied: if he didn't give her the job, she might run to Ted, which would've killed their friendship once and for all). She got her apartment (which was apparently in a bad neighborhood, considering that Ted's advice for her to "get a dead bolt" was appended with "if you want to live"), couldn't make it in finance, and had to move back to Ohio.
 * A less negative WMG is she just got transferred to another city. Alternately, Ted isn't the kind of guy that hangs around with his kid sister. Alternately Alternately, Unreliable Narrator -- she doesn't factor into any of the plots so she doesn't appear. Alternately Alternately Alternately, they couldn't get the actress back/didn't want to hire a new regular/semi-regular.

Ted's dad and Marshall's mom hook up at some point
Just shooting blanks in the dark guys. But it would make Ted and Marshall bros-in-law.
 * That would fit the Uncle Marshall and Aunt Lily thing. Now we just have to find a way to get Robin and Barney related to Ted...
 * "Uncle" and "aunt" are often honorary titles. Whether or not the WMG is true (I personally doubt it, just because it'd be really contrived, what with them living in completely different places and all), there's no reason for any of the characters to end up being related to Ted.

Lily and Marshall are terrible parents
It's show on several occasions ("The Murtaugh List", "Big Days" and "Baby Talk" being the only examples I can think of at the moment) that they can't seem to agree on a lot of things regarding raising/having kids. And they're already trying to have kids as of "Bad News". So when they have kids, the disagreements are gonna pile up, they're gonna fight about it all the time, and it's gonna take its toll on the poor kid.
 * Not to be a nitpicker, but their level of disagreement is pretty much par the course, even unusually mild, for most expecting couples. If there's one thing all parents can tell you, there is absolutely no way to draw up a good plan for raising kids and then stick to it.

HIMYM is a project designed to break the record of 'Longest running series'
It's been going this long and we haven't met the mother yet, but that doesn't mean meeting her will mean the end. There's still potential to show off the courtship, which could last for years, and then the marriage before the kids, then when the kids are born. 2030 is actually the planned final year of the show, and then it could still keep going by ending the flashback and just watching the lives progress from that moment.

The Captain is Barney's dad.
I got nothing. Just a verrrrry wild hunch.
 * That got Jossed a while back. Barney's dad is being played by John Lithgow. Sorry, but good guess anyway.

In the song "Nothing suits me like a suit" Barny had a valid (to him) reason to turn down each temptation

 * What would you do if you had to choose Between your suits and a pot of gold?
 * Barneys suit collection is worth more
 * What would you say if you gave your suits away in return you’d never grow old?
 * Barney doesn't have any problem with aging and figures it'll improve his dating.
 * What would you pick one million chicks or a single three-piece suit?
 * Barney loves the hunt, the rewards not as sweet without the hunt
 * Alternatively, Barney's exact line, "it's moot", implies as such because with his suits, Barney can already get one million chicks.
 * What if world peace were within your reach?
 * GNB makes most of it's profit on war and world peace would result in Barney out of the job

One of Teds future girlfriends will be played by Olivia Wilde.

 * Ted already dated Cutthroat Bitch and is currently in a relationship with Cameron, so going for Thirteen doesn't seem like a stretch.

Ted went to Cornell University for his master's degree in architecture
We already know that Lily, Ted, and Marshall went to Wesleyan University for their undergraduate degree. Marshall went on to Columbia for his law degree. Lily's career means a degree in education or art, or art education, for which a bachelor's suffices. In order to sit for his architecture exams, Ted would have to have an advanced degree in architecture, which Cornell University offers. But why think Ted got his degree their?

In "How Lily Stole Christmas" (2x11), Barney gets very sick and passes out at Ted, Lily, and Marshall's apartment. He's then seen being mothered by Robin and he's wearing sweatpants and a Cornell Big Red Bear t-shirt, specifically one with the huggy bear. You think it's Barney's? Heh. Please. He doesn't own a t-shirt. Sweats? Never. And anyway he's in Ted's bed. So is it Robin's or Ted's?

In the very next episode, "First Time in New York", we see Ted wearing the t-shirt in a flashback while killing a spider. Bam! Ted earned an advanced degree in architecture from Cornell University! My alma mater, bitch! And it's a master's degree, because their Ph.D. program is in the history of architecture and urban development or in historic preservation planning, both of which are totally Ted's thing because he's a giant architecture\history nerd. But the fact is that Ted's a practicing architect (and at one point a professor of architecture) both of which are compatible with a master's degree. Also, Ted's given charge of building a frickin' skyscraper at the age of 28, which suggests several years of professional development.

The Hulu Girl was the Slutty Pumpkin.
Just to be a bastard to Ted. One of his potential mothers and potential soul mates was there the whole time, and because of Barney he never got a chance to meet her. Also, would make the 'Barney is God' fanboys shut up.'
 * I second that thought. Despite being at the same party, Ted and her never interact. She's obviously hot too, which I recall Ted's description of the Slutty Pumpkin to be. I think it's kinda though, as the actual Slutty Pumpkin is played by an entirely different actress (I admit it's a long time since I've watched the first of the two Slutty Pumpkin episodes)

The title is a clue.
How I MET your mother, meeting the mother will be at "The Met" or something to do with The Met. Possibly a Mets game instead?
 * Ted meets the mother at, which takes place in a church.

Barney's father is in fact Julian Assange.
They look somewhat similar...

Ted, Marshall and Lily keep in touch with Maggie for many years later
More of a stray observation as opposed to a theory. When you see the futureforward scene in 5x10, when Ted says 'Maggie's window never opened again', you see three adults, in addition to Maggie and her husband playing with the kids, a redheaded woman, a brown-haired man and another man with black hair, ie. Lily, Marshall and Ted.

Marshall and Lily either are or want to be swingers.
It would explain the whole "find another couple" thing. Of course, Ted obfuscates this in his narration.

Sarah Michelle Gellar will appear at some point
Come on, it's the Whedonverse reunion series. Bonus points if she never interacts with Lily.
 * And she's The Mother thus causing another series where it's her fault Alyson Hannigan becomes unemployed.

Ted is either directly or indirectly responsible for all of his on-screen past girlfriends finding their soul-mates
Victoria met Klaus because of how Ted dumped her. Stella got back together with Tony, because Ted invited him to the wedding. Cindy realises who she really loves after briefly dating Ted. As as we now know

Robin's obsession with guns in particular stems from the time her father literally dropped her in the middle of the Canadian wilderness with only a knife.
Holding and firing a gun gives her the feeling of security and human advantage that she didn't have when it was knife versus teeth and claws. If that hadn't happened, she might have channeled the obsession she later had with guns into one or more other violent masculine interests in addition to hockey (emphasis on violence, such as mixed martial arts, masculine is only there as a category).

Robin's obsession with guns is directly because her father would have liked her better if she'd had a Gun In Her Pocket.
We know that it canonically and partially stems from her issues with her father, but it's possible that she subconsciously considers them a symbolic prosthetic penis, rather than just a power-tool and confidence enhancer.

Marshall and Lily's child will be named after Marshall's father
Unless there's a twist and they end up having a girl.
 * And since Marshall's brother is named Marvin Eriksen Jr after their father, Marvin Eriksen Sr, the baby will be called Marvin Eriksen Sr Jr!
 * The baby is officially named

Doug (the violent bartender) didn't actually say anything about Stella leaving Ted
Ted just told his kids that, to justify punching him. After Doug gives a very well placed speech about how friends should stand up for each other, I just feel that it was a bit out of place to give Ted that kind of mental kick. His friendly act towards Marshall afterwards shows that he has a sense of honor (Marshall backs up his friends, Doug respects that). I don't think Doug would pull that out, even in disappointment, when he had already taken an obviously superior stance to Ted and Barney. It is a perfect justification to throw a punch though.

Ted will have to become an insanely awesome friend before he can meet the Mother.
Ted seems to have been in a slump of concealed depression since "The Best Man" (at least), expressing deep-seated misery and grief (The Best Man, The Ducky Tie), acting grouchy and reserved (Disaster Averted), seeming lonely and frazzled (The Stinson Missile Crisis, Noretta), behaving like a desperate slut (The Slutty Pumpkin Returns), etc. He will pull himself out of his spiral of gloom and self-pity by embarking on a huge bid to make his best friends' dreams come true -- he'll play matchmaker for Barney and Robin and save the day during the birth of Marshall and Lily's son (we know from the flashforward in The Naked Truth that the birth is interrupted by some chaotic disaster), and it will spur him into fulfilling his explanation from Wait For It: "but there's a longer story, the story of the man I had to become before I could meet her" -- he'll finally emerge into the real, best version of Ted Mosby, who's worthy of the Mother's love. Remember in "False Positive", when Ted took charge and started fixing all his friends' problems and was awesome and insightful and astonishingly good at it? It was a clue to where Ted's strengths as a character lie, and would also explain why he's spent so much time rambling about his friendships when he's supposed to be explaining how he met their mother -- he needed the kids to really understand the fivesome in order to understand why he and their mother fell in love.

Robin isn't actually
. However, the scare will lead her and Barney to think about their future, thus leading to their wedding and eventually, a family.
 * Sorta.

The Manhattan of How I Met Your Mother really has Alien Geometry.
Lily's and Marshall's flat in Manhattan really did shrink while they were in their house in Long Island.

The reason Ted acts so much like a dad despite not having kids is because he was Promoted To Parent when he was younger.
Sort of a mild Fridge Horror: Ted's younger sister Heather is/was a completely irresponsible and uncontrollable near-juvenile delinquent. Someone who Ted's parents, who are detached, vacillating, uncommunicative and evasive (as well as, especially in his mother's case, completely oblivious and self-involved Cloud Cuckoo Landers), have never demonstrated the backbone or directness to discipline and control. If they are so incapable of communicating and facing difficult subjects that they never even got up the nerve to tell their kids they got divorced, could they possibly be the kind of people who could confront their daughter about her behavior? (Hell, she probably got that way to begin with because they never talked to her.) So maybe, because his parents refused to acknowledge that Heather was a mess, Ted did all the guidance and looking-after for his sister to make sure her entire life didn't implode and that she had to deal with some kind of authority, and developed his premature paternal characteristics because of it. It also gives a reason why he seems so much more like a parent than a sibling towards her.

This, or something similar, will be the last scene of the series.
(For easiness, the kids are being called Luke and Leia.)

"Ted: And that, kids, is how I met your mother.

(pause)

Luke: Dad? Can we go?

Ted: (sighs) Yeah.

(Luke and Leia quickly run off to the kitchen)

Leia: Oh my God, I thought he'd never stop!

Luke: It's a good story, but he could've skipped ahead a little bit.

The Mother: (walks in) Has Ted finally ended the story?

Leia: Yes, finally.

Luke: He went overboard on the backstory.

The Mother: Well, backstory makes any story more interesting. My story of how I met your father has a lot of backstory.

Luke/Leia: (exchange Oh Crap looks)

The Mother: Let's see... I think it started with meeting my friend Beck...

Luke/Leia: (try to make a run for it)

The Mother: No, no, sit down, this is a good story!

Luke/Leia: (sit down, looking like they're about to cry)

The Mother: Now, it all started in the summer of 1998.

Ted: (standing in the doorway, watching) Aaaaand that's why I love her.

(cut to credits)"


 * Damned good one, man. Might as well make the spin-off: How I Met Your Father.

Ted got the idea of telling his kids about how he met he met their mother from Robin.
Some time after Robin tells the others  (we know she will at some point, because Ted wouldn't have been able to tell the story otherwise) she will probably tell Ted about how she   Ted will remember this, and think about how lucky he is to have his kids, and decide that that's the way he's gonna tell them the story too.

Scott will show up again later in the series...
And receive a punishment of epic porportions for throwing a party in Marshall's house after leaving the poor guy stranded on the roof. Even better, it will seem like Scott has gotten the best of them all yet again, only to reveal it was all part of a complicated gambit to get him into trouble. Since the gang's made up of adults and he's just a teenager whose probably gotten in trouble a lot in the past, no one will believe he was framed.

Barney's Last words will be...
"Bro, I'm dying. It's the awesome unknown. It's gonna be Legen-" and then he will pass away. They will put his video will into a DVD player later and the first thing he says in the video will be "-dary!"
 * Shit, naw! That's how I'M going out!

The Wedding Bride was the result of Executive Meddling
Tony's not that big of a Jerk, but a big enough Jerk to just roll with it to get what he wants.

Goliath National Bank is not really that evil.
It's a heartless, moderately unscrupulous corporation typical of New York City, managed by typically selfish, ruthless businessmen. However, Ted's naivete about the corporate world, his distress over Marshall's misery about working there, Barney's constant hint-dropping and bragging about the mystique of the upper levels, and the fact that Bilson scrapped Ted's project and got him fired heavily colored his perception of the corporation. The passing of the years, and the gang's frequent and increasingly hyperbolic trashing of GNB in support of Marshall, allowed his memories of it to blur and mutate over time until by the year 2030, he remembers it as a LexCorp-esque Mega Corp of viciously evil Corrupt Corporate Executives who deal with the North Koreans, manipulate the economy, and plot to overthrow foreign governments.

Lily is an awful painter.
Minor one, but every objective source indicates that Lily really is pretty bad. Her painting instructor in San Francisco deemed her unteachable, the GCWOK thought the painting was bad and threw it away, and crazy sock guy said it wasn't very good. Karen also insulted it, but for some reason I am not inclined to mention it. The only compliments to her art I can think of come from Marshall and Barney, who are hardly objective.

Barney let himself get fleeced by Marshall and Lily when she painted his portrait.
His goal wasn't getting himself painted, but rather paying for Marshall and Lily's honeymoon. He knew they'd be too proud to accept that much money, and he's too proud to admit he supports them that much. When he said "You people are so easy to manipulate, dance, puppets, dance!" he actually meant that it was easy to manipulate them into accepting MORE money. Overly complicated schemes and supporting Marshall and Lily from the shadows are both things Barney does with alarming frequency. Also explain why doesn't make a bigger stink about the fact they did rip him off pretty severely. Also jives with the implication that Lily really isn't a very good painter.

Marshall Hates Backgammon Because He Can't Win At It
It's repeatedly shown that Marshall is extraordinarily gifted when it comes to playing games, but hates backgammon with a passion (the only good part is "gammon" in the name). For example, he picked up the bizarre tile/jelly bean game Barney played in "Atlantic City" and was able to help him win. He's also been shown to dislike the thought of the possibility of losing one hand of bridge (a game he has yet to learn and is clearly shown wrong) in a future imaginary scenario during "The Front Porch". Therefore, his hatred of backgammon probably stems from it being the one game he loses at.

Barney was in a boys' choir or had singing lessons as a kid
Barney is really good at singing. Obviously this is because Neil Patrick Harris is a trained singer, but in-universe Barney could have been trained too. Maybe his mum put him in choir to give him something to do while she went out with strangers, or maybe Barney just really want to be a singer, like how we know he wanted to be a violinist. Given his personality pre-suited up, it's possible. He can play the keyboard, too, so he's obviously quite musically inclined. Barney being Barney, however, he has never told his friends about this, because it would make him look un-awesome.

Robin likes her burgers well-done
It's why she always got her burger last in the best burger episode.
 * Alternatively, the rest like their burgers raw.