Sweet Polly Oliver

""As sweet Polly Oliver lay musing in bed,

A sudden strange fancy came into her head.

Nor father nor mother shall make me false prove:

I'll 'list as a soldier and follow my love.

So early next morning she softly arose,

and dressed herself up in her dead brother's clothes,

She cut her hair close, and she stained her face brown,

And went for a soldier to fair London town.""

- English Folk Song

A female character dresses up as a man to accomplish some end. Often becomes a variant of the Jackie Robinson Story. The sports version is especially popular in children's media, since it allows for an Anviliciously contemptuous boys' team for the heroine to win over with her talents.

Named for the old, old folk song "Sweet Polly Oliver" (quoted above), in which a woman disguises herself as a man so she can join the army and follow her soldier lover. However, the trope predates the name, going back apparently to a 6th century AD Chinese myth.

If a girl dresses like that all the time, she might be a Wholesome Crossdresser. Sometimes the audience (or a character) doesn't know this at first, and is surprised to find out Samus Is a Girl.

Contrast with Harmless Lady Disguise and Disguised in Drag. Some men may subconsciously see through this, and become Sweet On Polly Oliver. Since, in most cultures, she needs a new name, may occasion a Meaningful Rename. Not to be confused with Bifauxnen.

Many times when this is done in film and TV, the actress playing the crossdressing character rarely does a convincing job (see Hollywood Homely), requiring Suspension of Disbelief on the part of the audience that the other characters encountering her really believe she is a man/boy. On the other hand, quite a few women really did get away with this surprisingly easily in the past, which The Folklore of Discworld phrases as "in an age before unisex fashions, trousers meant 'man' and skirts meant 'woman'. Trousers plus high-pitched voice meant 'young man'. People didn't expect anything else, and saw what they expected to see." As a type of Weirdness Censor, the human mind will simply ignore small details that could give the ruse away, once it has classified a person as either male or female. And in societies in which male and female gender roles are clearly seperated with no room for overlaps, this effect would be even stronger, as the idea of meeting a crossdresser would be even more inconceivable than it is today.

You can listen to the full version of the song here.

Anime & Manga

 * Basara; The story takes place in a future Japan, reduced to a barren desert by a catastrophe at the end of the 21st century. The main character is Sarasa, a girl whose twin brother, Tatara, is prophesied to be the "child of destiny" who will bring back the country's independence and stop the tyrannical rule of the Empire, namely the Red King. When Tatara is killed, Sarasa pretends to be him in order to keep the downtrodden from losing hope.
 * In the first manga series of Sengoku Basara Ran Sei Ran Bu Kasuga disguises herself as her master Kenshin in order to serve as a decoy. Despite her huge assets she can still make a perfect performance.
 * One of the major plot points of Ouran High School Host Club, with the twist that Haruhi wasn't trying to pass as a boy, she was just wearing castoff men's clothing because she couldn't afford her school's expensive uniform, and didn't care enough to correct the members of the Host Club when they jumped to conclusions about her gender.
 * A continuing source of comedy is that the boys in the Host Club run themselves ragged to keep Haruhi's gender a secret from the rest of the school. Haruhi continues not to care. She only actively conceals her "secret" under threat of being fired.
 * Then again, Haruhi was never that feminine to begin with.
 * in Mai-HiME disguises herself as a man. In the German version of the dub, she's even given a man's voice (and not even a woman playing a man's voice, at that), as the production company was not aware "he" was actually female...
 * Akane from Ranma 1/2 disguises herself as a boy in order to battle the Yamata no Orochi without being eaten as the beast loves the taste of women. Similarly, Ranma's Unlucky Childhood Friend Ukyou "gave up" her femininity and passed herself off as a male (to the point of attending a boys-only school) after Genma and Ranma ran out on her marriage arrangement. Once her ruse is discovered, however, she quickly abandons the pose and crosses over into Wholesome Crossdresser territory (but only at school, her "civilian clothes" are all feminine even if she still acts boyishly); later that season (in the anime only) she even abandons that once, causing all of the boys at Furinkan High to wonder who the "cute girl" is. She wears the girl's uniform at least once after that (and lampshades it, naturally.)
 * And in a strange subversion of the trope, girl-Ranma had to disguise herself as male during a martial arts duel to hide the fact that she had been locked as female.
 * In Kaze Hikaru, the main character Tominaga Sei disguises herself as a male swordsman after the murder of her family to avenge herself on their killers, and ends up joining the Shinsengumi.
 * Michel Volban of Glass Fleet is a noblewoman who assumed her older brother's identity and his role as leader of La Résistance.
 * An early episode of Cardcaptor Sakura has a minor character named Yuuki dress up like a boy while she tries to remove a card's influence from her Disappeared Dad's painting. Sakura doesn't notice her gender until the girl's Nice Hat falls off and reveals her long hair.
 * In Cynthia the Mission Shii, the male 'protection' personality of the busty and beautiful Kanae manages to pull this off with a specific jacket designed to minimize her bust. It doesn't help that Shii acts very much like a man.
 * Subverted in Ludwig Kakumei.
 * Subverted in Girls Saurus, where all the other students at the boys' school Tsubasa goes to are convinced he's actually a girl pretending to be a boy, even though he isn't... Except for tough guy Arahata, who refutes the idea as ridiculous. "What do you think this is, a shoujo manga?" Of course, then when he goes to confront Tsubasa on the matter, he's utterly convinced that he's a girl after one look at him, too. He also gets molested by men on the train to school.
 * Subverted in Shugo Chara: When Nadeshiko's "twin brother" Nagihiko shows up in one episode, it seems painfully obvious, that it is her in disguise...
 * Done in the Sailor Moon manga by Minako. She uses the Crescent Compact to transform into a male Mugen Gakuen student so she can slip into the school and watch the concert of idol Mimi Hanyuu, who is secretly Mimette.
 * In the manga, both Nephrite and Sailor Moon did this--Nephrite as a ghostly bride, and Sailor Moon as the ghostly bride's groom.
 * Shizu, Mariya's twin sister in Maria Holic is doing the exact opposite of her brother by playing out this trope. None of her antics over at Mihoshi no Mori Boys' School have been seen, but this is especially troubling for Shizu since she Does Not Like Men.
 * Yellow successfully passed herself off as a boy for the bulk of Pokémon Special's Yellow chapter. Most characters didn't find out until the Gold and Silver chapter, though.
 * RED (and the cast introduced in the GSC Arc) didn't know Yellow was a girl until the end of the GSC Arc. Most everyone else already knew by the end of the Yellow Arc.
 * Otogi Zoshi: Hikaru disguises herself as her brother, because he is sick . The series loses a bit of charm when she drops the disguise.
 * Mizuki Ashiya from Hana Kimi who dresses up as a guy to get together with her favourite high jumper, Sano. They get close enough that people mistake them for Yaoi Guys and even Shuichi (the loud guy...) starts liking her thinking she's a guy, leading to some odd situations to say the least.
 * Kiri in the manga Never Give Up poses as a male model so she can stay close to her neighbor and love interest, Tohya. It helps a lot that Kiri already looked just like her dad, who was a model too.
 * The incredibly Bifauxnen Oscar of Rose of Versailles dresses as a man for her day job of commander of the Royal Guard. The rest of the time, she just does it because her father raised her as a boy.
 * Candy in Candy Candy is grounded during a school festival, but a friend of hers sneaks her a box with two outfits: a female gown and a male disguise, both with matching wigs. She uses them to sneak away and have fun without being caught by the school staff, alternating between the girly girl facade and the boyish one. Hilarity Ensues.
 * Kyouko from Skip Beat does this when she is challenged to act as the challenger's son.
 * Rei Saotome in Yu-Gi-Oh GX pretended to be a boy in her first appearance. Like in the Cardcaptor Sakura example, she's found out when she loses her hat and this reveals her Rapunzel Hair.
 * Part of the backstory for Override of Transformers Cybertron was that she somehow disguised herself as a boy to enter the great race for planet leadership. The weird bit, aside from the concept of a crossdressing robot, is that Override is pretty damn androgynous anyway and is a male in the original Japanese.
 * "Pierre", actually Valerie, is a villainous version on Agent Aika, whom the titular character falls for.
 * Practiced en masse in Ooku: The Inner Chambers because of a Gendercide plague that has wiped out most of the Japanese male population.
 * Manhwa:
 * Love In The Mask: Hyu-Bin is essentially forced into being a boy in order to be an effective bodyguard for a wealthy girl the same age. While Bodyguard Crush does no ensue, even the guys think "he's" pretty.
 * He's Dedicated To Roses: The heroine is a very plain girl who becomes a very pretty boy in order to escape her Rich Bitch "owner". Somehow no one notices her huge stash of stylish male clothes despite her being a servant.
 * Boy Of The Female Wolf: The Hot Blooded heroine ditched her femininity (except for the part that likes guys) after her mom left her to marry someone else and she has despised female "weakness" ever since.
 * In Naruto the male daimyo Sagi is eventually revealed to in fact be his twin sister Toki. After her brother's mysterious death, she swore to avenge him; to do so, she assumed the role of her brother and claimed the body that was interred was herself. Once her family's enemy was revealed and eliminated she revealed the truth of her deception to the people and continued in her role as daimyo.
 * In Girl Got Game, Kyo is forced/convinced by her father to pretend to be a boy so she can fulfill his dreams of playing basketball. She also lives in the boy's dorm with a boy she hates
 * This series is pretty much a parody of the genre. Similar to the example in Mulan, Kyo has many severe male stereotypes she tries to emulate with little success. She ends up adapting, however, and wonders if she can ever go back to being feminine. Her roommate also has an interesting way of coping once he discovers her true gender.
 * Charles/ Dunois of Infinite Stratos disguises herself as a boy while attending the school.
 * In Claymore, Clare disguises herself as a man for a time in order to travel under the radar, even using her limited Shapeshifting abilities to elongate her vocal cords and deepen her voice.
 * Mayo Chiki's premise.
 * Itsuki Myoudouin from Heartcatch Pretty Cure, taking her big brother's role due to the aforementioned man having aweak heart. Said man is also a case of Dude Looks Like a Lady. He got better, and Itsuki was able to resume being a girl by the end of the show. It should be noted that while Itsuki is mistaken for a boy several times in the series, pretty much everyone in the school knows she's a girl. Not that it matters much ...
 * Tsukiko from Samurai High School switches places with her Half-Identical Twin brother Kou to enter said high school and become Supreme Commander of Japan. It helps that they both are adept at the opposite gender roles.

Ballads

 * In the Child Ballad The Famous Flower of Serving Men, the heroine's husband and baby are killed by her mother, and she disguises herself as a man to run away and work.
 * In the Child Ballad Child Waters, the heroine refuses to leave the hero, despite his declaration that he goes to woo another woman. He insists she dress as a footpage and run alongside his horse.
 * In the Child Ballad Rose the Red and White Lily, the sisters dress as men to escape the Wicked Stepmother and rejoin with their stepbrother lovers.
 * Yet another one (Robin Hood and Maid Marian) has Marian seek Robin, armed and in man's clothing, and when the two meet Robin is also disguised - so they fight, for "at least an hour or more", before recognizing each other.
 * Crossdressing is a classic folk music trope. One song, "The Soldier Maid," (not sure whether it's true folk or modern) is about a girl who joins the British army as a drummer boy, and is only betrayed when a woman comes on to her, learns she's female, and goes off to tell her officers. The officers are actually disappointed they have to send her home, and give her a bounty and pension for her service. The song "Cruel War," covered by Peter, Paul and Mary, focuses on a woman who follows her love to war and is killed while in disguise.
 * "Jackaroe" is another song about a girl who goes off to war to follow her love, this time in the Navy.
 * As is "Billy Taylor", but it has a twist ending. It turns out that the titular character, whom the song's main character has joined the Navy to follow has found a new girl, and the main character tracks them both down and kills them, and is promoted for it.
 * "The Handsome Sailor Boy" -- In which a young woman signs on a ship as a cabin boy and the captain falls in love with her. In some versions, she's looking for her lover and doesn't tell the captain she's a woman, until she's safe on shore. In others, she's just doing it for the adventure, both the captain and the captain's wife fall in love with her -- but it's only the captain who realizes she's a woman ... Until one night, on board ship, when she gives birth. Then everyone knows.
 * In "The Female Rambling Sailor", a woman goes to sea after her lover is pressed into naval service and drowns. She proves an exemplary sailor, and none of her crewmates suspect her identity until she dies in a fall from the rigging and they discover her 'female form'.
 * There's a Spanish ballad about a girl who dresses like a man, calls herself Don Martín and goes to war because her father is too old. Then, the prince falls for her (getting extremely confused because he somehow suspects "he" is a girl, but isn't quite sure). Then the prince comes out to the queen and she suggest several tests to expose Don Martín, all of which fail, except the last one: a bath. Don Martín runs away and the prince after her, and they marry.

Comic Books

 * The Sandman:
 * There's also Desire, who switches genders as necessary.
 * Marvel 1602: Carlos Javier has a page named John Grey. Scott Somerisle is insanely jealous of "John"'s friendship with Angel, much to the latter's confusion.
 * In Legion of Super-Heroes, Lightning Lass made her first appearance pretending (rather inexplicably) to be her dead twin brother, the Legionnaire Lightning Lad. The deception was exposed when Sun Boy noticed that she didn't have an Adam's apple.
 * In Justice League Task Force, there's Mystek, who wore a very masculine armored suit. One of her teammates, Triumph, found out the truth on a trip through space. Mystek, who got claustrophobic when in costume, hid in the bathroom to take it off. Triumph eventually demanded that she come out, having had enough time to "drain the weasel". He opened the door, saw the indignant lady inside, walked back to his seat in a daze, and whispered, "Mystek has no weasel."
 * The Spanish comic magazine El Jueves had a story, Emili a o where a girl, Emilia, pretended to a boy to do the mandatory conscription in the Army and be with her boyfriend.
 * Agnès de Roselande/Isabeau de Marnaye in the Francois Bourgeon's historical series Les Passagers Du Vent.
 * In one Weird War Stories, a drummer boy being held in a American Civil War prison camp turns out to be a girl, leading to a Sweet On Polly Oliver'' situation. And then zombies attack...
 * "Jack", in the Deathwatch comic strip by Paul Cornell (Elizabethan Judge Dredd), is quite clearly a girl wearing a false moustache to work as an actor. And, inevitably, ends up playing Helen of Troy in Faust. Surprisingly, while the Fish Out of Temporal Water acts as Only Sane Man to the Medieval Morons in just about every other respect, this is the one point where he has a blind spot as well.
 * Subverted in Demon Knights with the Shining Knight (who is a Sweet Polly Oliver in some other versions as well). Her costume looks convincing to the reader (due to the fact that she's very flat-chested) but fools no one in-universe.
 * As a young girl, Martha Washington in Give Me Liberty habitually passes herself off as a boy to avoid being sexually assaulted. She then gets grabbed by someone looking for young boys.

Fan Fiction

 * In The Lost Girl (Fanfic), Friendly has a variant of this, as she quickly forgets she ever was a girl.
 * There's more than one Axis Powers Hetalia fic out there that imagine the female Nations as being forced to do this out of necessity (i.e. avoid getting raped by their own soldiers), though this usually happens in historical-themed stories to stress the Values Dissonance.

Fairy Tales

 * In The Lute Player, the queen dresses as a man to get safely to her husband.
 * In The Girl Who Pretended to be a Boy the youngest daughter of an emperor disguises herself as a boy and rescues a princess.
 * The Brothers Grimm fairy tale The Twelve Huntsmen (who are actually a princess and eleven female companions disguised as men).
 * Several Italian fairy tales have this, ranging from going to war, saving a prince dressed as a doctor, escaping from villains, or simply because they feel like it/ a magic pony told 'em to.: Fanta-ghiro the beautiful, The Dragon and Enchanted Filly, The First sword and the Last broom, Wormwood, The King of Spain and the English Milord, the Great Narbone, (in universe) The Parrot, the Canary Prince....
 * In Costanza / Costanzo Costanza disguised herself to go into service because she could not get a suitable bridegroom of Royal Blood, only one of Blue Blood.

Film
"Norma: YOU NO GOOD TWO-TIMING SON OF A BITCH! HE'S A WOMAN!"
 * In Disney's Mulan, Mulan disguises herself as a man by making her hair shorter and wearing a soldier's outfit so that her disabled father won't have to go.
 * Yellowbeard: Spoofed; one of the ship's officers is named "Mr. Prostitute" and is an obvious woman with a fake mustache.
 * The stoning crowd in Life of Brian, which also doubles as Recursive Crossdressing.
 * In She's the Man (a modern-day retelling of Shakespeare's Twelfth Night, mentioned below), the main character disguised herself as a boy so that she could play soccer after the girl's team was canceled.
 * In the second Pirates of the Caribbean movie, Elizabeth Swann disguises herself as a man to sneak on board a ship. Since she changes on the ship itself, her dress is found by a few of the sailors, which leads to a mad rush to find the stowaway naked lady.
 * In the 1984 finnish comedy Uuno Turhapuro In The Army, the protagonist's wife takes her husband's place in the finnish army for a short while against her will, with an extremely unconvincing haircut and stubble. What really gets her, though, is that no-one noticed a thing...not even while they were bathing.
 * Viola in Shakespeare in Love, Shakespeare's Love Interest, who wants to be an actor. Hilarity and awkward situations ensue.
 * Yentl followed this trope. The main character became a man in order to attend a school in Jewish Talmudic Law, which was forbidden for women at the time. It made for some really weird love triangles.
 * In Carry On Jack, Sally steals Albert Poop-Decker's uniform and takes his place on the frigate Venus, while Albert finds himself pressganged onto the same ship as a common seaman.
 * The  from Pitch Black.
 * The Disney Channel movie Motocrossed involved a girl posing as her brother to enter a motocross race, after he breaks his leg. What makes this one more ludicrous is that the siblings have the same name (Andy, short for both Andrea and Andrew).
 * Not quite so ludicrous:
 * This trope is the central plot of Just One Of The Guys, an 80's teen comedy (and actually a half decent film).
 * After her rescue from Fogg's Asylum by Anthony in Sweeney Todd: The Demon Barber of Fleet Street, Johanna dresses up like a boy in order to hide from Judge Turpin.
 * Connie And Carla, about two female performers who witness a murder, so they go into hiding by disguising themselves as Drag Queens (a spoof of Some Like It Hot where two jazz musicians who witness the St. Valentine's Day Massacre go into hiding by joining an all-women's jazz band). In other words, they dressed up as men who dress up as women.
 * A similar idea is used in Victor Victoria, merely as a way to break into show business. The lead actress's (Julie Andrews) singing is apparently far more appreciated by audiences who think she's a gay female impersonator.


 * Happens in the third From Dusk Till Dawn movie.
 * The Swedish movie Mitt liv som hund (My Life As A Dog) is about a 12 year old boy sent to live with relatives in the countryside when his mother contracts tuberculosis. One of his new friends, who is also the top player on the local boys' football team, is actually a girl. Keeping up the charade becomes somewhat difficult when she hits puberty and things start to grow ...
 * Common in fairy-tale movies (Dragonslayer, The Brothers Grimm) as a way to conceal the gender of daughters who might otherwise be fed to dragons, kidnapped by witches, etc.
 * In the 1950 British thriller The Clouded Yellow, Jean Simmons cuts her hair and exchanges her dress for trousers in order to pass as "Master Fox". The disguise is never seriously tested, which is just as well as she's a remarkably unconvincing boy.
 * There is the 2003 Afghani film, Osama, the first film to come out of Afghanistan after the overthrow of the Taliban. The film is about a 12-year old girl who disguises herself as a boy in order to earn an income for her family, who are left destitute and with no way of earning an income after the death of her father and uncle. Osama is an unusually realistic example of the trope.
 * In the 1979 basketball comedy Fast Break, D.C. (Harold Sylvester) admits to Coach Greene (Gabe Kaplan) that he has unusual feelings for his (ostensibly male) teammate Swish. In the climactic game, Swish unwraps her breasts and hits the court. D.C. is relieved.
 * Princess Leia briefly disguises herself as the bounty hunter Boushh in Return of the Jedi, though this barely counts since he's also an alien.
 * And since, at least in the Old Republic, female soldiers weren't a rarity--there's female pilots in Episode I who attack the Trade Federation control ship, not even going into the Expanded Universe or female Jedi.
 * Ma Vie En Rose introduces such a character (a tomboy who goes by "Chris") right at the end,.
 * The Disney live-action version of Swiss Family Robinson has Roberta (or "Bertie") do this, as she and her grandfather have been captured by pirates. Not very convincing, and The Reveal shows that she's a girl when her head wrap is pulled off to reveal... really short hair, but a suddenly more girlish face.
 * The German film Schwarzer Jäger Johanna (1934), in which Marianne Hoppe plays a woman who joins the Black Brunswickers during the Napoleonic Wars to follow her loved one.
 * In Salt, Evelyn Salt disguises herself as a man in order to get into the White House towards the end of the film.
 * The Canadian Short "No Bikini" shows that bath and this trope do mix sometimes. Robin, a 7-yr girl, hates bikinis, but girls must wear a swimsuit for a swimming class. So she pretends to be a boy so she can attend just in swimming trunks.
 * The Whoopi Goldberg vehicle The Associate was a double version; she not only dressed as a man, but went white to win big in business.
 * The Challengers has a girl dressing up as a boy so she can play in the school band.
 * There is a Soviet comedy called My Dearly Beloved Detective about two female detectives with the last names of Holmes and Watson. At one point during an investigation they dress up to sneak into a club of bachelor men. The head of the club gets wind of this and states that all the members will undergo "an embarrassing examination"... which consists of every member being forced to give a gentleman's word he's male. Holmes passes. Watson is saved by a man in love with her who takes the blame.
 * Princess of Thieves centers on Robin Hood's daughter, Gwyn, who dresses up as a man to follow her father.
 * In another Robin Hood example, Maid Marian first appears dressed in armor and assumed to be male in Robin Hood Prince of Thieves.
 * Katharine Hepburn takes her turn in Sylvia Scarlett.

Literature
After the girl is discovered, the sultan is so impressed that he decides to make her a knight anyway, since she is the only one in the army who isn't a complete dandy. Dressed as a boy, she goes off on a quest which will win her the hand of a princess. She rescues the princess, and the princess discovers she is a girl, but they decide to get married anyway. ""In truth, young lady and gentleman, this has been a very childish affair, and to explain your folly and rashness there was no necessity for all this delay and all these tears and sighs; for if you had said we are so-and-so, and we escaped from our father's house in this way in order to ramble about, out of mere curiosity and with no other object, there would have been an end of the matter, and none of these little sobs and tears and all the rest of it.""
 * In The Breadwinner, a girl named Parvana, who lives in Afghanistan, disguises herself as a boy in order to earn money for her family because her father died and her brother was too young to provide for them.
 * The Harry Turtledove alternate history novel The Guns of the South features Molly Bean, a prostitute who disguises her flat-chested self as a man to serve in the Confederate States' unit Castalia Invincibles. She poses as her "cousin" Melvin Bean and joined because the war was taking away all her customers. Ignorant and illiterate, she learns to read and begins to fall for her teacher. How much combat did she see? She was at Gettysburg, y'all. She later serves a surprisingly vital role in defeating the AWB men who are time travelers, by being a popular bedmate while covertly spying on them. Her letters to her lover describe many futuristic marvels (None of which she understands, but her teacher/future husband twigs onto the fact that these guys are from the future). These prompt him to instruct her to go to Confederate President Robert E. Lee and describe everything she'd seen. She does, but her attempts to hide her womanly self make it difficult (Lee can't figure out why she keeps on mixing up "I" and somebody named Melvin in her story). After she helps take down the AWB, she marries her teacher. In Real Life, there was an actual Molly Bean who enlisted in the Invincibles, but she was discovered and sent home. Her livelihood as a prostitute was pure author's invention.
 * This is the main storyline of the historical novel Pope Joan (based on what may have been a Real Life example as well, but is generally considered fictitious).
 * The old man's granddaughter in Swiss Family Robinson who was disguised as his grandson.
 * Terry Pratchett's Discworld novel Monstrous Regiment spoofs the everloving hell out of this one. Our heroine Polly Perks joins the army of her war-torn home country of Borogravia, under the alias of "Oliver Perks", to look for her strong-but-simple brother Paul. . Pratchett also plays this for drama as much as for laughs, with Polly becoming disgusted by the contrast between how men and women are treated in Borogravia.
 * Oh, and the song exists in the setting. She took the name as a reference, but finds the joke gets old when people keep asking if she's heard of it.
 * What's really ironic is that when the regiment has to dress as women in order to infiltrate an enemy base, the male lieutenant is simply waved through, but Polly is assumed to be a man dressed as a woman and questioned.
 * The performing troupe of female impersonators in The Last Continent included an actual female, who was filling in for her brother.
 * And turned sideways because Rincewind honestly doesn't notice, though he did get upset that his (presumably male... ish) Luggage was now dressed in high heels (a lot of them) and a frilly pink tablecloth.
 * An obscure Pratchett use of this trope, from the Assassins' Guild Discworld Diary, reveals that a few Polly Olivers had enrolled in the then all-male Guild school, by means of a short haircut and a note excusing them from gym classes. One former SPO became head tutor for Black Widow House after the Guild school went co-ed, and now teaches Edged Weaponry and Fencing.
 * Alanna of Trebond from the Lioness Quartet books by Tamora Pierce. As a nine-year old she starts dressing as a boy in order to train for knighthood as Alan, and keeps it a secret until after she's already earned her shield (and thus is formally Sir Alanna).
 * Dernhelm/(Eowyn) from The Lord of the Rings is a classic example. In her Crowning Moment of Awesome, she is able to kill the Lord of the Nazgul precisely BECAUSE she is not a man.
 * The Witch-King's belief that no man could kill him came from a prophecy by Glorfindel a thousand years before. The prophecy said "not by the hand of man shall he fall." The Witch-King thought he was invulnerable, but he got shivved by a hobbit (not a Man) and his head struck off by a woman (not a man).
 * In the book Half Magic a young girl gets really annoyed at Lancelot so she wishes that she was his match in strength and skill, then conjures a suit of armor and challenges him to a duel. She wins and the crowd cheers her. When the king asks her to remove her helmet she does so, having forgotten she still looks the same underneath. As the mood of the crowd shifts from shock to anger, she's called names and Lancelot is jeered for being beaten by a girl, for all of five minutes before Merlin erases everyone's memories.
 * The main character of this story in the Livejournal-based "webzine" Imaginary Beasts.
 * In the children's picture book Little Kay a girl dresses up as a boy to become a knight. The king somehow finds out there's a girl among the men, and asks his advisers how he can figure out which one she is. (This being a children's book, I guess we're supposed to assume the king is too stupid or prudish to go with the obvious.) In an inversion of the Achilles myth, the advisers suggest offering jewels and pretty fabrics and so on, on the assumption that the girl will be the one interested. Since this is a comedy, though, the men all turn out to be raging dandies who love the gaudy stuff while the girl spurns it. The only one who offers useful advice is the castle maid, who suggests the king have them all drink a toast, since when they all tilt their heads back to drink the men's Adam's apples will be apparent. This proves effective.
 * Possibly based on a Russian fairy tale - at the end of that story, the king asks the girl to bathe with him, she goes to change... and runs off, leaving a note behind saying "by the way, yes, I AM a girl."
 * There is an Italian tale which has the same scene (except the girl fakes an urgent message forcing her to return home). It seems to have inspired [[http://en.wikipedia.org/wiki/Fantaghir
 * There was a similar fairy tale, only that the whole group was a bunch of girls. When they got wind of the 'tests' to expose them, they would try to confuse things even more. When offered jewels and fabrics, some of them ignored them, some of them appraised the valuables, and a couple of them 'stole' some of the gems. When ashes were strewn across the threshold (on the assumption that the girls would try to clean it up), most of them marched right across it, while a few of them tried to clean it up and made the mess worse in the process.
 * In The Mother-Daughter Book Club, one character wears a boy's uniform and helmet to try out for the school hockey team, since the coach refuses to let a girl join. Naturally, her skills secure her a slot on the team, even after her identity is revealed.
 * In The Girl Son, Imduk, a Korean girl is disguised as a boy so that she can attend school, at a time when it was believed only boys could learn the Chinese language, with the approval and knowledge of the school's principal.
 * Rune, from The Lark And The Wren, passes as a boy to join the Bardic Guild, which only accepts men. Somewhat subverted in that she's fairly open about her gender with most people not directly connected to the Guild.
 * Considering they were planning to castrate "him" to keep "his" pure voice, this may have been a better fate.
 * It turns out well enough in the end:.
 * In The Zucchini Warriors, one of Gordon Korman's Macdonald Hall books, the star of the Macdonald Hall football team is in fact Cathy Burton from the girls' school across the road, wearing the name of school nerd Elmer Drimsdale (who has to keep up the ruse out of uniform). The resulting fame goes to his head a little.
 * ZICTORY!
 * In the third Finnegan Zwake novel, Uncle Stoppard's novel uses this with Ophelia/"Osric". Seriously.
 * In the novel The Shakespeare Stealer a girl disguises herself as a boy so she can be an actor, since it was illegal for women to perform on the Elizabethan stage.
 * Exactly the same thing happens in No Bed for Bacon, the novel upon which Shakespeare in Love was (very) loosely based.
 * Esther Friesner's Majyk by Hook or Crook and Majyk by Design feature a Welfie swashbuckler who prefers to be called "A Blade for Justice".
 * Pamela Kaufman's Shield of Three Lions has the main character, a young girl, dressing up as a boy to save herself from being killed off or married for her property. She ends up going off to the Crusades and falling in with King Richard. Among other things, he falls in love with her as a boy and there is much confusion and danger (since he's the king) when he realizes she's a girl.
 * Bloody Jack is a young adult novel about a London orphan girl who joins the Royal Navy as a ship's boy. Risky, but much more attractive than dying of starvation. This causes problems both comedic and poignant when she, etc. It has several sequels, and the character sometimes reverts to this trope in a pinch, even though by then she's filled out a little more and presumably no longer looks like an androgynous eleven-year-old. People still buy it, though.
 * Nearly every character in Piers Anthony's Refugee (in the series Bio of a Space Tyrant) ends up dressing as a member of the opposite gender as a defense against ubiquitous space pirates.
 * In John Barnes's One For The Morning Glory, Calliope dresses as a man. Characters pretend to be deceived. Sometimes even she forgets that she's dressed as a man and glares at people who refer to her as male.
 * The main character of Isabel Allende's Daughter of Fortune goes off to California disguised as a man in order to find the lover who left her to seek his fortune there.
 * Didn't anyone else read Cue for Treason in high school?
 * Buran in Barbara Cohen and Bahija Lovejoy's Seven Daughters and Seven Sons disguises herself as a boy in order to make her family rich, since her father has no business sense. Sweet On Polly Oliver ensues.
 * Princess Miriamele in Tad Williams' Memory Sorrowand Thorn dresses as a servant boy when she wants to roam the Hayholt unrecognized, making this a cross with King Incognito. Her disguise is effective enough that the hero, Simon, is fooled (granted that he's not all that observant when it comes to girls), even after they meet in the wilderness. Wiser characters do see through it, though.
 * One of the tales in Boccaccio's Decameron features a daughter of the King of England traveling to Italy disguised as an abbot. She falls in love with a young fellow she meets on the way, but he is quite disturbed by her advances until she places his hand on her chest.
 * In One Corpse Too Many, the second Brother Cadfael mystery by Ellis Peters, Godith Adeny (daughter of Fulk Adeny, foe of King Stephen of England) does this by dressing like a novice monk to prevent capture by the king, which would have caused her to be held for ransom. Cadfael deduces who she is quite quickly in the book. In the TV show of the book, he sees through her disguise instantly. As does the audience.
 * In a later novel, done again by "Brother", and this time the ruse is successful. Even Cadfael is completely fooled until almost the very end of.
 * Gawen in Jane Yolen's Sword Of The Rightful King turns out to be, who wants to join the Round Table to get revenge upon Sir Gawain. The Reveal is a great relief to Arthur, partly because but mostly because.
 * Lampshaded with Blabbermouth in Haroun and the Sea of Stories by Salman Rushdie. "Don't you know girls have to fool people every day of their lives if they want to get anywhere?" When her secret is revealed, the only character bothered by it is quickly chagrined by someone more awesome who isn't.
 * In The Anubis Gates by Tim Powers,  does this in order to infiltrate London's criminal underworld and track down the unnatural creature that killed her fiancee.
 * Eponine in Les Misérables for a while - she trades outfits (with a boy who is actually described as enjoying crossdressing for a lark) to disguise herself so she can sneak into the barricades. Marius doesn't even recognize her when she, but that might just be him being a silly, tactless and clueless emo kid.
 * Partly subverted in Swedish author Ulf Stark's Dårfinkar och dönickar, in that the crossdressing is initially a mistake - Simone is assumed to be a boy called Simon. She becomes increasingly invested in her disguise as the story progresses, though.
 * Another Swedish example is Caroline in Maria Gripe's Skugg-/Shadow books, who spends large parts of the books pretending to be a young man called Carl. She does it for several reasons: increased freedom, to gain a certain job, and for the sheer heck of it. She will also quite happily flirt with both men and women. (Which backfires when two of them fall deeply in love with her and decide to marry each other, bonding over their mutual love for Carl. Yeah.)
 * Joanna Sedley in Robert Louis Stevenson's The Black Arrow may be the least convincing example of this ever. Everyone who sees her realizes that she's a girl, except for the protagonist, who thinks his new friend is just really wimpy.
 * Stevenson didn't put too much effort into it for two reasons: 1) He was writing it as part of a serial, and having her listed as a boy for the first few installements (it originally appeared in a weekly kids' magazine) would have confused the readers, and 2) he was only writing it for a quick buck while he wrote Prince Otto. Ironically, The Black Arrow ended up being much more popular.
 * Arya Stark in A Song of Ice and Fire sort of had this trope forced upon her, although she was something of a tomboy in the first place.
 * In the first book, her unkempt, tomboyish appearance leads to lots of people mistakenly calling her "boy", and she angrily corrects them. In the second book, once she's in disguise, she repeats her catchphrase with a twist when someone sees through her ruse: "I'm not a girl!"
 * Brienne is an interesting case in that she does look like a tall, powerfully built man ; she would have a harder time trying to look feminine than passing as a man. As she's one of the strongest knights in the Seven Kingdoms, she was able to secure a place in Renly's guard without actually needing to hide. The only way you could tell her actual gender is by seeing her bareheaded, which logically leads her to keep her helmet on when she'd rather not be recognized.
 * While it hasn't been explicitly revealed as of yet, the half-Summer Islander, slim, smooth-faced Dornish Alleras with the widow's peak who's not interested in women bears a striking resemblance to the half-Summer Islander, slim, Dornish female Sarella whose father had a widow's peak.
 * Michelle, the main character in Elaine Moore's Get That Girl Out of the Boys' Locker Room, becomes this trope so she can play on her school's boys' football team.
 * Deryn/Dylan in Scott Westerfeld's novel Leviathan disguises herself as a boy to join the air forces.
 * Nastily subverted in Iron Dawn, in the backstory of Barra the Pict: seeking her fortune in the male-dominated Mediterranean, she dresses up as a young man and joins a group of bandits. She need not have bothered, as the thugs were disappointed to discover that she wasn't a boy when they turned upon and gang-raped her.
 * Marion Zimmer Bradley's wizard Lythande is a woman who disguised herself to be able to learn magic; by the time her teachers found her out, she had learned too much for them to send her away. Instead, her punishment was that if any man should learn she was a woman, she would lose her powers, thus condemning her to continue the masquerade for the rest of her life.
 * In one of the Star Wars novels, Princess Leia debates trying to pass herself off as a man. She takes a good, long look in her mirror, and decides her figure is far too emphatically female. (Probably intended as an ironic reference to her Sweet Polly Oliver turn in Return of the Jedi)
 * Kite from Sewer, Gas and Electric acted out this trope during the American Civil War.
 * Iain Banks's adds a twist in that the protagonist herself isn't aware of this. Yes, it's a weird book.
 * In Stephanie Kennedy's 1980s YA novel Hey Didi Darling this trope is the main plotline. A Girl Group decides to dress up like boys and form Tommy & The Tigers in order to get gigs.
 * Miranda, the title character from Lane Robins' novel Maledicte, passes herself off as a young man to get revenge on her lover's father. The male name and pronoun are used even in scenes from "his" point of view, which definitely makes for some odd sex scenes. Actually, the entire book is an odd experience - Maledicte's deception is so complete that the reader forgets that it is a deception.
 * Judith, the teenaged protagonist of the young adult novel The Minstrel's Tale, is forced into an Arranged Marriage by her stepfather. Not only is she deeply put off by her bridegroom, who is at least thirty years her senior, but on the night of their betrothal dinner she falls in love with the young minstrel who comes to play and sing for them. He leaves her an instrument and a note suggesting another way of life, which she accepts gladly; she cuts off her long hair, dresses in clothes belonging to her deceased brother, and runs away to minstrel school.
 * In My Father Had a Daughter, a fictionalized account of the life of Judith Shakespeare, the heroine dresses as a man in order to sneak off to the Globe Theater and act in her father's plays. Works well until he figures out who she really is, but even he has to admit some amusement at the trick. The narrative implies that her ruse was his inspiration for Twelfth Night (see the Theater section below).
 * In Rose Daughter, a retelling of Beauty and The Beast by Robin McKinley, Beauty's sister Lionheart disguises herself as a boy so she can get a job and help support her father and sisters. This confuses their new neighbors somewhat, who are quite sure that when the family moved in there were three daughters rather than two daughters and a son, but they shrug it off and go about their lives.
 * Another Robin McKinley example occurs in The Outlaws of Sherwood, when a young woman named Cecily joins Robin's band under the name Cecil. She remains undiscovered for quite a while, which is particularly impressive considering her brother Will is also in the band. And Marian disguises herself as a man for a shorter period in the same book.
 * In the final book of the Prydain Chronicles, Princess Eilonwy dresses as a man so she can go off to war with Taran and the others. Something of a subversion, since she fools absolutely nobody who knows her, but they sort of roll their eyes and put up with it because there's really nothing else they can do at this point.
 * In the Ursula K Le Guin short story Dragonfly, Irian dresses as a boy in order to accompany the sorcerer Ivory to Roke, the wizard's school only boys are allowed to attend. Of course, Ivory's got his own agenda and.
 * There's a Spanish-language writer of historic novels, who was a BIG fan of this trope. Almost every novel has a girl impersonating a pageboy, either to follow him to war, to deliver a message, and even so a boy can take her clothes and escape from jail impersonating her.
 * Show Within a Show example: In Gilded Latten Bones, one of Jon Salvation's comic plays used this trope, starring a princess who was raised as a boy and crowned king by her unsuspecting subjects. Apparently this trope hit it off big in TunFaire, as lots of other playwrights immediately stole the idea and wrote their own variations.
 * In Poul Anderson's A Midsummer Tempest, Jennifer dresses as a boy to escape her captors.
 * Scyla in Shadows of the Apt
 * In Sarum, Aelfgifu dons Saxon armor to fight a skirmish against the Vikings and is initially mistaken for a young man, as she'd intended. Subverted in that her deception never fools anyone for long, but she fights well enough that her brothers insist she be allowed to participate in the Battle of Edington without having to invoke this trope.
 * In the historical novel The Tokaido Road (by Lucia St. Clair Robson), the main character Cat travels through feudal Japan dressed in several male disguises. It seems that a lone female traveler would be unusual but not impossible; the real reason for the cross-dressing is to evade a warrant for her arrest.
 * In an interesting reversal of the Attractive Bent Gender trope, Cat's love interest sees her as an attractive male monk and considers taking "him" to bed. Once the love interest discovers Cat's true identity, he's impressed and has no problem transferring his attraction onto the true female version.
 * Alice in Beth Hilgartner's A Murder for Her Majesty takes this up almost by accident. Having witnessed her father's murder, apparently at the Queen's command, she needs to find a place to hide; conveniently she has a run-in with some helpful boys in the cathedral choir, who think it would be great fun to disguise her as a choirboy.
 * In Robin Hobb's Ship of Magic, after Althea runs away from her family, she asks a friend for advice on how to find work as a sailor on her own merits; the friend snarkily responds that she would have to find a way to be reborn as a boy, preferably one with a different last name. Which is exactly what she does - she disguises herself as a boy, and joins a crew under an assumed name.
 * Rosario in The Monk, who quickly soon reveals himself to be a woman named Matilda.
 * Don Quixote plays this trope perfectly straight with Dorotea, a girl who dress as a man who sets to get back her unfaithful lover in the first part of the novel. At the second part, this trope will be parodied and deconstructed
 * The daughter of Don Pedro de la Llana parodies this trope showing us will use it in Real Life: The Ingenue who has been in a Gilded Cage all his life and asked his brother to show her the world… that is, the little town they live… at night. She dresses as a man because she wants to hide her identity. But nobody knows her because she had been hidden all her life. Justified because she is Just a Kid who has lived in a Gilded Cage and she really doesn’t know better. As Sancho said:

""A woman and a Christian, in such a dress and in such circumstances! It is more marvellous than credible," said the viceroy."
 * Clingy Jealous Girl Claudia Jeronima deconstructs this trope: She is wearing man’s clothes because she has murdered a supposedly unfaithful lover and Barcelona is having a Civil War. She wants to conceal her identity so her family would not be harmed by Revenge.
 * The Exile Ana Felix deconstructs this trope: Fleeing for Spain for having muslim fathers, she enters Algiers, where the King blackmails her to steal his family treasure hidden in Spain. So she wears man’s clothes to come back with the King’s soldiers and mislead the Spanish authorities. She is captured by them and threatened with execution when she declares she is a woman:


 * Ruth Mallory in Someone Elses War. She doesn't get the idea until someone else mentions it, however, and wishes she had thought of it much sooner.

Live Action TV

 * Farscape did this in the episode "Coup By Clam," when Moya was orbiting a planet notorious for its torturously sexist laws. When a tech was sent over to help, Chiana found "him" attractive... and when it was discovered that the grease monkey was a Wrench Wench in disguise, Chiana wasn't bothered by this at all. Unfortunately, the security guard accompanying the tech wasn't so understanding, and came within inches of killing her before Scorpius intervened.
 * Actually, Chiana, being the experienced Lovable Sex Maniac she is, knew the tech was a Sweet Polly Oliver from the start and just used the ruse of hitting on her to get the mechanic to reveal herself. As Chiana herself put it "I know a man when I see one."
 * Spoofed by the character of 'Bob' in the various Black Adder series.
 * Queenie makes a very poor attempt at this (wearing a big cloak over her elaborate dress) in an attempt to join in on the boys' drinking party.
 * Also used for a bit of subtle Character Development; in the second series, when 'Bob' first shows up, Lord Blackadder is both taken in by Bob's disguise and highly attracted to him, prompting something of a crisis of sexuality. In the fourth series, 'Bob' shows up again... and Captain Blackadder's not fooled for a second. Unfortunately, his superior officer is...
 * In Star Trek, Ferengi society is highly sexist, and female Ferengi are denied the right to work, do business, or even wear clothes; naturally, in one episode of Star Trek Deep Space Nine, the plot revolves around a crossdressing Ferengi woman.
 * And in another, Quark not only crossdresses but actually gets a sex-change in order to seduce a businessman into supporting female enfranchisement. Squick, squick, squick.
 * Quick note about the Ferengi: To them, not doing business is more sexist then not wearing clothes. Their hat is capitalism, after all.
 * In the 2006 Robin Hood a Saracen woman called Saffiya disguises herself as a boy called Djaq. It takes the Sheriff of Nottingham several episodes to guess she's a woman and (season 2 spoiler).
 * Another Robin Hood variation; in the 1991 TV movie Robin Hood with Patrick Bergin in the lead role, Maid Marian (Uma Thurman) attempts to escape an Arranged Marriage to the evil Sir Miles Folcanet by disguising herself as a boy and joining Robin's merry men. When the Sheriff of Nottingham attempts to lure Robin into a trap by having his lover impersonate Marian, Marian is forced to reveal herself to Robin to save him. She was more successful at impersonating a guy than the above example, partly because Uma's fairly tall.
 * In the '90s Fred Savage sitcom Working, Chris Grant (short for Christina) shows up for an interview to join the office where the show is set. The boss is a known philanderer and "good old boy," so Christina dresses and acts masculine to get on the boss's good side and score the job. Hilarity Ensues when her gender is revealed to the main character (but not the boss), and then they all hang out in a sauna. Even more Hilarity Ensues after Chris is found out, gets fired, and the office rises up against the boss's unfair hiring practices. In the next round of interviews, he's forced to consider females for the job. The woman he chooses to hire is actually the main character in drag.
 * Dee in the Its Always Sunny in Philadelphia episode "The Gang Gets Invincible".
 * This being It's Always Sunny, and Dee being... Dee, as soon as she takes off her disguise, she breaks her foot while trying to kick a football.
 * Many Korean Drama's loove this trope:
 * The First Shop of Coffee Prince has this trope as its main plot.
 * Korean drama (and a Japanese remake) Hana Kimi, with a girl pretending to be a boy to go to an all-boy's school to meet the high jumper she has always admired. Of course,
 * Also the heroine in the Korean drama The Painter Of The Wind.
 * The titular heroine of the Korean drama Queen Seondeok.
 * In yet another Korean drama, Han Guk Young, Sujeolnyeo Seo-ssi (Lee Tae Ran) dresses like a man and goes out spying at night.
 * You Are Beautiful has the heroine pretending to be her teenage heartthrob brother in order to take his place in a boy band. Jeremy's reaction to her reveal is priceless.
 * Amusingly subverted in The Curse of the Clawepisode of Ripping Yarns (a parody of "The Monkey's Paw") with a character who only appears to be an obvious Sweet Polly Oliver because her strict Victorian upbringing was so strictly Victorian she doesn't know she's a woman (or indeed what women even are) (The hero is happy to enlighten her.)
 * In the second season of Twin Peaks,.
 * In the Chilean Soap Opera Pampa Ilusion, the female lead is a young and beautiful doctor who wants to get close to her misogynistic Jerkass of a father, who disinherited her and her Missing Mom when she was born. To do so without being found out, she crossdresses as a male physician, and unwittingly attracts men (like the male lead, who is her dad's business counselor) and women (like the old man's house maid)
 * Brazilian miniseries Copas De Mel had a woman disguising as a man to travel with the Brazilian team for the 1958 FIFA World Cup. On renaming, she decides to use the same nickname as her actual, Mel - from Amelia to Melchiades.
 * The Young Riders: Pony Express rider Lou was really Louise, and managed to keep her real gender hidden from most of the main characters for nearly the entire first season (and from some of them for even longer.)
 * Her love interest,  Kid, learns her secret in the very first episode and agrees to help her keep it. (It's the shared secret that helps them bond together).
 * On the first episode of The Suite Life On Deck, Bailey disguises herself as a boy to get into Seven Seas High. The program accepts both genders, but by the time Bailey applied they were out of spots for girls.
 * In Daddy's Daughters, Eugenia (Darya Melnikova) disguises herself as a boy to help the school win a football match in Episode 35. It helps she was a Pettanko Bifauxnen early in the show's run.
 * Tom, Leo's fellow apprentice in Leonardo, is a girl who disguised herself as a boy to escape an arranged marriage and because in Renaissance Florence girls can only paint as a hobby. Her real name is Lisa, which given the series' In the Past Everyone Will Be Famous tendencies, presumably makes her Lisa del Giocondo. (This is confirmed in Episode 8.)
 * Jacqueline, alias Jacques, a woman disguised as a man while on the run for murder, in Young Blades. Although in her case, it's a Paper Thin Disguise.
 * The Disney made-for-TV movie Motocrossed does this when Andrea Carson must fill in for her injured brother Andrew Carson in a motorbike race. They get away with it because of their similar names; she signs up as "Andy", and while the other racers are male, the form doesn't require a gender.
 * In the Darkest Africa sketch in episode 29 of Monty Python's Flying Circus, the explorer called Brian is obviously Carol Cleveland disguised as a man, though no special attention is drawn to it.

Mythology & Folklore

 * Older Than Print: Earlier than the Trope Namer is the Chinese legend of Hua Mulan, a woman who joined the army as a man in lieu of her father, which has been made into a Disney movie, Mulan. This story was first recorded in the 6th century C.E.
 * Another old but non-military Chinese example, the Butterfly Lovers: Zhu Yingtai, who disguised herself as a man to become a scholar. She fell in love with her slightly clueless roommate Liang Shanbo and arranged to have him marry her 'sister.' This does not go as planned.
 * The most commonly accepted explanation for the name of Petit Jean Mountain in Arkansas is that a young French lass dressed as a cabin boy ("Little John") to be near her fiance, who was a sailor on a ship headed to the New World. She caught ill and died, and her alleged grave can still be seen on the mountain.

Tabletop Games

 * In Traveller, both the Aslan and the Sword Worlders have specific rules for this. In both these cases this is not a disguise so much as a formalized way to allow vocational flexibility in females without hurting the traditions. In the case of the Aslan it comes about when there are no male heirs and a female has to "become male"; which includes not only carrying out male roles but vowing celibacy. In the Sword Worlds it is a way for eccentric women who actually want to go adventuring to do so without hurting the Stay in The Kitchen principle.

Theater

 * Shakespeare loved this one. As You Like It, Two Gentlemen of Verona, Twelfth Night, The Merchant of Venice, Cymbeline... Remember that the women would have been played by men in the first place, and you can just imagine the potential.
 * English Renaissance drama in general does this frequently for precisely that reason. And after women were allowed to act on the English stage in the 1660s, playwrights continued to include this as part of the plot as a form of Fan Service.
 * Happens fairly regularly in Opera -- Beethoven's Fidelio, for one.
 * Poor Zedenka (Arabella, Richard Strauss), forced to dress as a boy because her family cannot afford to let her doll up like her big sister Arabella. She gets her man in the end, so all is well.
 * Handel's opera Alcina. Brave girl Bradamante dresses as a man, under the name Ricciardo, to save her lover Ruggiero from the clutches of the sister witches Alcina and Morgana. They both fall in love with "him". A messy love network ensues.
 * The plot comic opera The Firefly has pretty little street singer Nina run away from home to Bermuda disguised in boy's clothes. Unfortunately, the boy in question happens to be the notorious pickpocket Antonio Columbo.
 * In the comedy A Servant of Two Masters, one of the "masters" is a woman disguised as her own brother, trying to find her beloved - who is the other one.

Video Games

 * In Assassin's Creed
 * If the player has a sufficiently tuned 'babe-dar' then the player likely noticed how feminine the target was in the cut scene before the battle even commenced.
 * Faris from Final Fantasy V. Yes, 'his' secret is outed very early on, but she doesn't start dressing any differently.
 * A bug (maybe?) actually creates one in Final Fantasy Tactics. The first stage of the Deep Dungeon/Midlight's Deep occasionally spawns a "male" Time Mage... who Screams Like A Girl, literally. If Invited into your party, you'll discover that she's actually a female unit in everything but in-battle appearance; she can use female-specific equipment and can access the Dancer class (but takes on the appearance of a Bard when she does), and she is susceptible to Steal Heart from male units (and, if taught the ability, can use the same skill on them.) She even gets female sprites in the formation menu; just not in battle.
 * In the video game The Legend of Zelda: Ocarina of Time Princess Zelda disguises herself as a warrior named "Sheik" to hide from the main villain and help the main hero. The reveal was a big surprise to players when the game first came out, but now it's so well known you can even have her switch back and forth between the two personas in the Super Smash Bros series.
 * On the other hand, people are still trying to discern whether Sheik is male or female; (S)he's almost as confusing as Birdo... and the manga adaptation doesn't help matters either.
 * of Persona 4.
 * Despite appearing as an enemy, King was handled as this in the original Art of Fighting -- her reason in this case being that due to not being able participate in Muay Thai tournaments as a child due to her gender, she passed herself off as male and continued to do even after moving to the United States. Later games made her femaleness more obvious, even including visible breasts -- although relatively modest-appearing... despite the fact that without binding and concealment, her bust measurement rivaled Mai Shiranui's, which was capitalized on for some fanservicey official art, and occasional in-game fanservice. King of Fighters 2001 threw this muted handling of her appearance completely out the window, but we don't like to talk about it.
 * In the first game, King's gender was a Tomato Surprise that you could uncover by defeating her with a fireball attack. Too bad her hit cries were so feminine that it hardly counted as a secret.
 * In Fate Stay Night, Saber is actually
 * Jayle, one of the Einherjar in Valkyrie Profile is a woman disguised as a male soldier. Interestingly, her commanding officer discovers this, but keeps his mouth shut because they've fallen in love with one another. She's more conspicuously outed just before her death, when a sorceress's seduction spell, fails to entice her. It did however entice that commanding officer, who runs her through.
 * Jade Empire features a theatrical production in a culture where only men may be actors; naturally, if the player character is female, she takes the part anyway. Of course, it's a a female part...
 * Sypha Belnades in Castlevania III: Dracula's Curse. Being a witch, she had to disguise herself to avoid being burned. The game and manual were fairly good about concealing this fact until the very end. Judgment, however, gives her large breasts and a fanservicey outfit.
 * In Dragon Force (the game, not the band), one of the leaders is a female who wears intimidating and bulky armor with a face-concealing helmet for the first half of the game. Her proper gender is indicated immediately if you play as her in the campaign, but nobody else knows until she takes off the helmet.
 * In Rival Schools, Akira goes undercover in a body-concealing motorcycle helmet and leather jacket to investigate her older brother's disappearance. This is necessitated by the fact that her brother attends an all-male school for Delinquents.
 * A common trope in the early Metal Gear (particularly in Metal Gear 2: Solid Snake, Metal Gear Solid, and Metal Gear: Ghost Babel) had Solid Snake having to rendezvous with a female ally who has already infiltrated the enemy by disguising herself as a soldier. Particularly in MG2 and MGS, the only way to determine who is Snake's contact is to follow said contact to the Ladies' room.
 * Or if the player is detail oriented, they may notice that the actually-female soldier sways her hips as she walks, and has slender legs. Snake himself notices it, a fact which is later given a nod in Super Smash Bros Brawl when he realizes immediately that Samus Is a Girl.
 * In Metal Gear Solid 2, Olga Gurlukovich disguises herself as a Cyborg Ninja similar to Gray Fox from the first game, while disguising her voice and using the alias of Mister X.
 * In Da Capo,
 * Leucos in the latest Glory of Heracles game tries this to escape from authorities, but she doesn't pull it off well, and the game's characters (and even the tutorial) lampshade this.
 * In the obscure Sierra adventure game Peppers Adventures In Time, the titular character disguises herself as a boy for about 90% of the game, considering that she time travels to the American Revolution.
 * Cocona from Ar Tonelico 3 disguises herself as to avoid being detected as a reyvateil.
 * in the first Galaxy Angel game is made to crossdress for political reasons.
 * in the original Tokimeki Memorial because apparently her father wanted a boy.

Web Comics

 * Spoofed here in The Whiteboard.
 * Timothy Peter Hugo Stanley. "A few crewmembers are convinced he harbors some deep secret, but... it remains a mystery." Beneath is an obvious picture of a (not-very-Foglioesque) girl.
 * Emet from Warrior U dresses as a boy so that she can learn to become a warrior.
 * In Strays, Meela's brother cut her hair so they could pass as brothers, rather than the brother and sister their enemies were looking for. She didn't like it.

Web Original

 * Huge Schoolgirl Dacey "Dawson" Ashcroft in Survival of the Fittest pretends to be a guy due to the negative attention she received in her previous school, feeling it easier to get through highschool if everyone believes her to be a man. Luckily, she doesn't look all that feminine, and unlike some of the other female Southridge students lacks large breasts.
 * Amber Jarrett in Decades of Darkness

Western Animation
"Zapp: (after the Leela feminine reveal) I've never been so happy to be beaten by a woman!"
 * In the Futurama episode "War Is the H-Word", Leela disguises herself as a man named "Lee Lemon" in order to join the army. Zapp Brannigan is still attracted to her without seeing through the disguise leading to some... confusing feelings.


 * Clone High: The Joan of Arc clone disguises herself as "John Dark" ("Jeanne d'Arc") to join the hoops team, to give them a fighting chance against their rivals.
 * The whole thing is mocked in a leaked production piece; apparently a future storyline had Joan becoming prom queen. The position of Prom King was given to basketball star John Dark. She ends up awkwardly dancing by herself during the prom royalty dance.
 * This is actually based on her historical actions, although the real Joan made no secret of her gender and wore male clothing just because it was more practical.
 * Although it's a pretty safe bet that the real-life Joan's army had no dolphins disguised as people.
 * Gummi Bears -- Princess Calla does this to avoid getting a bodyguard. Her father finds out and so is impressed at how formidable she is that he immediately agrees that she doesn't need one.
 * The Disney movie based on the Mulan legend, referenced above.
 * In one episode of The Simpsons, Springfield Elementary becomes segregated by gender. Since the girls' school isn't teaching math properly, Lisa disguises herself as a boy in order to join the boys' class.
 * Sam(antha) in Danny Phantom briefly disguises herself as a boy to trick three female ghosts who have made all the men disappear. Her presence was to get the three to use their powers so Sam's team could counter with their own weapon to restore all the men back.
 * By day Cybersix disguises herself as a male high school teacher.
 * Combined with You Go Girl on Doug when Patti tries out for the softball team.
 * An episode of Jimmy Two-Shoes had Heloise disguise herself as a boy in order to see a list of "Guy Stuff" that Jimmy and Beezy wouldn't let her see.
 * An episode of The Grim Adventures of Billy and Mandy has Mandy disguising herself as a boy calling herself Manfred to help out Billy's baseball team which does poorly, he won't let her join because he doesn't want a girl on his team despite Mindy leading the team that always beats them, she only wears pants and a baseball cap, once she takes off the cap he recognizes her and kicks her out only to accept her again when she puts the cap back on (he's pretty stupid).

Real Life

 * During the American Civil War, some of the corpses of fallen men were discovered not to have been men at all. At least 240 women are known to have served in the ACW disguised as men, as you can read about here: http://www.amazon.com/They-Fought-Like-Demons-Soldiers/dp/1400033152/ref=pd_cp_b_1 Several maintained their disguises after the war in order to qualify for pensions. It was a lot easier for women to get away with this back in the days before routine physical examinations, since often the only physical standards enlistees had to meet were "upright and breathing". Also, many 18th and 19th century women were relatively small-breasted due to inadequate nutrition, and many figured out the trick of padding out your waist instead of trying to completely eliminate your breasts, which was helped by often ill-fitting uniforms.
 * Joan of Arc did not disguise herself as a man, but chose to wear men's clothing while fighting for practical reasons.
 * Deborah Sampson disguised herself as a man and served in the Continental Army under General George Washington from 1782 to 1783.
 * There are over 22 documented cases of women serving in the Prussian army during the Napoleonic Wars.
 * One woman made it to sergeant major before she was wounded and uncovered.
 * The most well-known was Eleonore Prohaska, who served as private August Renz in the Lützow Free Corps and only revealed her real identity when she was mortally wounded in the battle of the Goehrde (1813). A few more:
 * Louise Grafemus (born Esther Manuel), a converted Jewish mother of two, who served with some financial backing from Princess Marianne of Prussia as an uhlan during the Wars of Liberation (1813-1815), in search of her husband who, as it turned out, was serving in a Russian unit and was killed before the war ended. Grafemus was wounded more than once, promoted to Wachtmeister (sergeant-major) and is claimed to have been decorated with an Iron Cross.
 * Auguste Krüger, served in the Kolberg Infantry Regiment 1813 to 1815, rose at least to Unteroffizier (sergeant), awarded an Iron Cross in 1814. She continued to serve even after she was discovered to be a woman.
 * Maria Werder, the wife of a landed gentleman, served as a hussar to be with her husband in the campaigns of 1806/7 and 1813. She was promoted to Wachtmeister in the 2nd Silesian Hussars and and revealed her real identity only when she left the army after her husband was killed in the battle of Leipzig.
 * Nadezhda Durova, the Cavalry Maiden, was the first Russian female officer. During the Napoleonic wars she disguised herself as a man to enter military and had a distinguished career even after her actual gender was discovered.
 * Plus Mary Read and Anne Bonny, two Sweet Polly Olivers on the same ship, no less! Apparently the practice of women joining pirate crews disguised as men was common enough for Black Bart to specifically forbid it in his formulation of the pirates' code. Ironically, both escaped hanging because they claimed to be pregnant, since it was a pretty standard way of forestalling a death sentence, as there wasn't any immediate method to definitively confirm the allegation. Read later died of a fever while in prison, while Bonny disappeared from the record.
 * Not to mention that Bonny was hitting on Read, and ended up having A Bridget Dropped On Her, after which she revealed her own disguise and Dropped A Bridget On Read.
 * Read went on to fight a duel to save another (presumably) male pirate she was interested in. She allegedly won the duel by tearing open her shirt and then skewering her opponent while he was distracted.
 * Mollie Bean, who is known only from an 1865 article in the Richmond Newspaper, after she was discovered. She served in the 47th North Carolina Regiment disguised as a boy for over two years. Was included as a character in Harry Turtledove's The Guns of the South.
 * Also Catalina de Erauso, "The Lieutenant Nun".
 * Mexican female writer Sor Juana Inés de la Cruz, back in the 17th century, crossdressed in order to sneak into an university back when women were not allowed to receive education. She later decided to become a nun and spare herself from The Reveal.
 * The book Female Tars: Women Aboard Ship in the Age of Sail by Suzanne J. Stark gives several examples of women who joined the British Royal Navy in disguise (as well as exposing a few frauds). Includes a detailed autobiography of Mary Lacy, who served as a seaman and shipwright for twelve years.
 * A non-military example: Billy Tipton, a noted jazz pianist who was found to be biologically female at death. Tipton had a long string of relationships with women, including one long-term relationship with an experienced prostitute who never knew Tipton was not 100% male. That takes talent.
 * Norah Vincent posed as a guy for one and a half years, exploring the male-only parts of the society (including a Catholic cloister) out of pure scientific interest. Nobody guessed his her game the whole time.
 * James Barry, a nineteenth-century British Army surgeon, was born Margaret Ann Bulkley. Margaret Bulkley became James Barry in order to be accepted into medical school, then maintained that identity throughout a long and distinguished military career. Barry served all over the British Empire for fifty years, and worked hard to arrange better sanitation, food, and medical care for soldiers, prisoners, and civilians alike.
 * Charlotte "One-Eyed Charley" Parkhurst, a stagecoach driver during the Gold Rush, who wasn't publicly outed until after her death.
 * The legend of Pope Joan I and only, the sole female Pope.
 * It's common in Afghanistan for mothers with no sons to dress young girls as boys to escort women of the family and support the family. Mothers with no sons are often pitied, and having what looks like a boy in public improves their image. Then the "boys" suddenly have to become wives, without knowing any domestic skills or even how to wear a burqa...
 * There is a small rumor that the warlord Uesugi Kenshin of the Sengoku Period was a woman masquerading as a man. Sengoku Basara and the live action drama Fūrin Kazan reflect this by depicting Kenshin as apparently male but beautiful and androgynous.
 * Let's not forget Hatshepsut, Egypt's female King.
 * And Cleopatra, for that matter, who often wore a false beard and dressed in male clothing.
 * This used to be common in the Royal Navy. So common that chiefs would regularly shout Show Some Leg to make sure a given sailor was male before sending him to work.
 * After the Battle of Trafalgar a naked women was found floating in the wreckage by sailors of the HMS Pickle. They chivalrously gave her some clothes and listened to her story. She was sailing with her husband in disguise aboard the French ship Achile. When her ship caught on fire she removed her clothes and jumped overboard. She swam toward some shipwrecked clinging to a spar. When they kicked her off she floated in the water until she was picked up by the British. The story ends with a Crowning Moment of Heartwarming for her husband was among the prisoners and was reunited with her.
 * Albanian sworn virgins are women who took a vow of virginity and became a man in the eyes of the society. There are many reasons for that: no male heir, escape form arranged marriage or poverty, when only men can actually work. Although their oath is usually taken in the front of family or local community, most of the sworn virgins don’t bother to inform newly met people about their true gender. This can lead to some embarrassing situations e.g. during hospitalization.
 * Jeanne Baret, the botanical assistant, housekeeper, and possible lover of the French naturalist Philibert Commerçon, accompanied her master when he joined the Bougainville expedition; since women were not allowed to serve on French ships, she traveled in disguise under the name of "Jean Baret". Despite the thin pseudonym, Commerçon pled ignorance when the deception was revealed.