Improv

Improv, short for Improvisation, is the act of going off-roading from the set script and making up entire chunks of dialogue or characterisation. This is similar to an ad-lib (a short -- usually one or two lines -- deviation), but here the connotations are that it happens frequently, if not actually the entire acting method. This varies wildly from individual lines to half of the script. When an entire production is based around improvisation, you're probably looking at a variant of Theatresports.

Many examples of Throw It In are because of this, with the actor just goofing around with the script in between takes. It can also be used to produce Enforced Method Acting, if one actor is turned loose to improvise in order to get a realistic reaction from another actor.

One way to see where a show or movie tends to use this is when there are Hilarious Outtakes and a certain line changes depending on the take that was used.

Compare Harpo Does Something Funny where the script has a gap left with only the instruction "[actor] does something funny here."

Film
"Ringo:: Is it cold in here, or are we just practicing to be Canadians?"
 * Most Judd Apatow productions rely heavily on it. In fact at least Undeclared hired its cast based entirely on their skills in it. Apatow even said that he nicknamed the camera technique the "Segel Cam" after how long the actor Jason Segel could go on improvising.
 * A lot of Jack Sparrow's mannerisms were not actually written into the script, but improvised by Johnny Depp. Sparrow's epic ending line "Now, bring me that horizon" was also an improv.
 * In fact, Depp's whole demeanor differs greatly from the creators' original vision of the character; he was intended as a far more conventional dashing rogue. When Depp interpreted the character differently, Michael Eisner even went so far as to say he was ruining the film. Depp's response was essentially "Trust me or fire me."
 * Depp said himself that he chose to add the 'campness' as he thought that the other actors applying for the role were better than him. He chose to just go crazy and have fun.
 * He also claims that his portrayal of the character has liberal doses of Keith Richards mixed in.
 * And then Keith Richards was cast as Jack's father. Win?
 * Apparently the reference to Will being a eunuch was also an improvised line that was kept in the script, and expanded upon as a Running Gag.
 * Charlie Chaplin was renowned - and hated by his crew - for this. He would often begin the shoot with no script, instead making up and trying stuff on the fly until something worked... Which some days, wouldn't happen. He also had a bad temper which showed when he got frustrated not being able to find just the right gag.
 * Of course, Charlie Chaplin is still Charlie Chaplin. There's a set-piece gag in The Great Dictator where Chaplin's barber shaves a customer in time with the (frighteningly fast) Hungarian dance on the radio. The intention was to do the shave repeatedly and then patch it together with the music in editing. Chaplin had the music playing on-set, though. Result: The shave was filmed perfect in one take. The first one.
 * Buster Keaton generally worked from an outline instead of a complete script, and was famous for playing baseball with his crew while waiting for inspiration to strike.
 * In Three Ages, Buster attempts to jump from one rooftop to another using an improvised springboard and doesn't quite make it. Instead of reshooting they kept the fall and created a sequence involving multiple awnings, a drainpipe and a firefighters' pole to get the character to ground level in one piece.
 * Nick Frost ad-libs during the scene in Shaun of the Dead, where Ed describes the pub regulars in an effort to cheer Shaun up. There are several different takes of the scene where he describes the old woman as an ex-pornstar, all apparently unscripted. Simon Pegg's laughter is genuine as a result of this.
 * Certain short, one-or-two-minute scenes in the Austin Powers movies were edited together from literally hours of footage of the actors improvising off each other. One scene of note was the initial scene at the Evils' table in Goldmember, where Seth Green and Mike Myers just kept on playing until the cameras ran out of film.
 * In Give My Regards to Broad Street, many of Ringo Starr's lines are ad-libs. Possibly the majority.

"Garth: Did... Did you ever find it attractive when Bugs Bunny dressed up like a girl bunny?
 * Peter Sellers often improvised on set, though he was more careful than most to do so in character. Stanley Kubrick used three cameras to shoot his Dr. Strangelove scenes so the best material could be edited together; most famously, much of the hotline telephone monologue is said to be improvised, as is the behavior of his Evil Hand in the second-to-last scene.
 * When Sellers is doing the aforementioned evil hand scene, you can see the guy who plays the Russian ambassador trying his hardest not to burst into fits of laughter, complete with shaking and much biting of the lip.
 * In the final scene, Dr. Strangelove suddenly stands up and screams "I can walk!" delightedly. Supposedly, Sellers forgot that Strangelove was supposed to be a cripple, and shouted out the line to cover his mistake.
 * The most spectacular Sellers example might be The Party, which was mostly improvised from an outline provided to him and the other actors with the director's help.
 * In Being There, his response to the television producer's declaration of how many people will be watching him and the producer's reaction are also ad libs.
 * Most of R. Lee Ermey's dialogue in Full Metal Jacket was improvised, thus making him one of the very, very few actors allowed to go off-script in a Kubrick film. Allegedly, after the first take featuring the line "I'll bet you're the kind of guy that would fuck a person in the ass and not even have the goddamn common courtesy to give him a reach-around!" Kubrick approached Ermey and asked what the term meant. Ermey explained. Kubrick's reply was something to the effect of "Oh. Do some more of that."
 * Most of the dialogue in Iron Man was ad-libbed with encouragement from director Jon Favreau who approved of the "naturalistic feel." The film was subjected to so many numerous re-writes that the script changed daily. In the end, scenes were shot with a skeletal script outlining important plot points and action with the actors creating the lines as they went. Robert Downey Jr., who joked about balling up the script and throwing it against the wall on numerous television appearances, was credited for improvising many of the movie's notable moments, including Tony Stark's speech for the "Jericho" demonstration and getting the reporters to sit on the floor at the press conference.
 * In fact, according to Jeff Bridges, there was no actual script at all, and the entire movie was improvised. Bridges said he had problems getting his head around this style of filmmaking until he told himself to think of it as "a $200 million student film".
 * In The Usual Suspects, Fenster's bizarre mumbling accent was entirely improvised by Benicio del Toro, who felt the character as written was boring and one-dimensional. With the change, it ended up being del Toro's first breakout role.
 * Pretty much all of Bill Murray's dialogue in Tootsie is supposedly improvised.
 * Ditto for Kingpin
 * Ghostbusters is famous for blurring the line between ad libs and scripted dialogue, with nearly half the dialogue cited as ad libs by the cast. Examples include the famous "Twinkie" scene, Peter's response of "so do I" when Egon says he blames himself for not testing their proton packs, and Egon's response of "that would have worked if you hadn't stopped me" when Peter refers to a Noodle Incident involving Egon trying to drill a hole in his head. Sigourney Weaver's ad libs include comparing Peter to "a game show host" (the original line was a used-car salesmen, but she observed that he actually bounces around like a game show host), and much of Rick Moranis's dialogue as Louis welcomes people to his party is improvised.
 * According to the commentary track on Spaceballs, Rick Moranis ad-libbed the entire "Dark Helmet playing with his action figures" scene.
 * One of the most famous comedy line improvs appeared in the movie Waynes World. During a scene where the main characters Wayne and Garth are sitting atop their car watching airplanes take off, when suddenly Garth asks a strange question:

Wayne: No.

Garth: Neither did I, I was just asking..."

"Um, well, ordinarily when you make glue first you need to thermoset your resin and then after it cools you have to mix in an epoxide, which is really just a fancy-schmancy name for any simple oxygenated adhesive, right? And then I thought maybe, just maybe, you could raise the viscosity by adding a complex glucose derivative during the emulsification process and it turns out I was right."
 * As it turns out, the entire exchange was improvised. Dana Carvey, Garth's actor, visibly snickers right before asking the initial question and Mike Myers bursts out laughing after responding. The director decided it was too funny to cut and so left it in the final version.
 * The famous "you talking to me?" monologue in Taxi Driver was completely improvised by Robert De Niro. The original script just said "Travis looks in the mirror".
 * Most of the dialogue between Bing Crosby and Bob Hope in the "Road To" movies was completely ad libbed, to the point that Dorothy Lamour often found herself unable to get in her lines. In The Road To Morocco Hope and Crosby share a scene with a live camel which decided to spit in Hope's face. The "attack" and Crosby's resulting ad-lib went into the film.
 * While not a great film, The Score did have its moments. Several of them were the back and forth between Robert De Niro and Marlon Brando, who were purposely given only key points to hit in dialogue and then simply left in front of a camera.
 * In the film of Buffy the Vampire Slayer (as opposed to the TV series) this also comes up in what is probably the film's single genuinely funny scene. Buffy, played by Kristy Swanson, stakes the Big Bad's (Rutger Hauer's) second in command, who is being played by Paul Reubens. The scene as written simply required Reuben to say "You're gonna wish you died" and then slide out of shot. Which he did. And then, two seconds later, stood up again with stake still in his chest, putting on a bunch of fake but hilarious "ah, ooh, eee, ah, ooh!" noises and even looking directly at Swanson for one second before going off at it again. The fact the shot was ad-libbed is clearly visible in Swanson and Hauer's faces: Swanson turns to someone offscreen as if querying what's going on -- and the shot cuts to Hauer, on whom another camera was already rolling, and who has a vaguely amused look on his face and who shrugs as if to say "Just roll with it." Which they did, and the shot stayed in. A part of the performance even got into a postcredits sequence.
 * In Gremlins the script had very little written for the Gremlins, so the voice actors made up a bunch of stuff they thought was funny for them to say; Frank Welker (voice of Stripe and others) said that he just made a bunch of random noises into the microphone. The recording staff thought it was so good they decided to leave it in and had the others follow on his example.
 * In Mars Attacks no dialogue was written for the Martians so Frank Welker made up his own language for them.
 * In Saving Private Ryan, the whole anecdote about the girl and the barn was ad libbed by Matt Damon.
 * In Romy and Micheles High School Reunion, Lisa Kudrow made up the entire glue formula on the spot.


 * Another famous example of improv is the Mockumentary This Is Spinal Tap. The movie had no script; the actors simply got into character and improved for hours. Rob Reiner shot several hours of footage which was distilled down into the movie itself; hours of outtakes have been included on the various DVD sets.
 * Christopher Guest, Michael McKean, and Harry Shearer found they enjoyed this formula so much that they went on to make a number of other improv-ed mockumentaries, including Waiting for Guffman, Best in Show, A Mighty Wind, and For Your Consideration. Most of the ensemble cast in these movies started out in improv comedy groups such as the famous Second City.
 * Tommy Lee Jones reportedly didn't have much respect for the scripts of Men in Black and the sequel, and made up most of his lines as the camera rolled.
 * He may have had more respect for the script of the The Fugitive, but he did the same thing while filming it--ad-libbing what became his character's defining line (and the film's most famous)--"I don't care!". And the fugitive himself, Harrison Ford, deliberately did not learn the lines for the scene where he's interrogated by the police, wanting his responses and reactions as their questions and attitude change from helpful to hostile to be as realistic as possible.
 * Ford did the same thing in the original Star Wars, not learning his dialogue for the scene where he tries to respond to a call to the detention cell.
 * John Rhys Davies in The Lord of the Rings. Many of his lines were this, including the one during the drinking game in Two Towers when he says that "It's the Dwarves that go swimming with little hairy women".
 * Doubles as a Shout Out, since he was basing it on a line from Jaws

Live Action TV
"Jenna Fischer: "Those looks of shock/giddiness/confusion on our faces are real. We were all on the edge of our seats wondering what would happen next. I can't believe we held it together for as long as we did. I'm not sure we've ever laughed so hard on set.""
 * Their was a short lived partially improvised Sitcom called On The Spot hosted by Chip Esten and Starring Jeff Davis.
 * The scripts of The Mighty Boosh are only loosely written, usually only specifying a few things the actors need to say to further the plot, with much of the rest being improvised. The performers often change their lines between takes to keep their delivery fresh. This is even more the case with the original radio show which was less rehearsed than the TV show.
 * Outnumbered, a British sitcom about life with three kids, uses a fair amount of improvisation. It produces remarkably realistic acting from the child actors, as they're allowed and encouraged to say things in their own words.
 * Whose Line Is It Anyway easily popularized the knowledge of improv games to general audiences.
 * Evidently, the same can be said of The Drew Carey Show, who had quite a few cast members translate between the two shows. The "Drew Live" episodes were at least partially improvised.
 * As well as its spiritual successors Drew Carey's Green Screen Show and Improv-A-Ganza.
 * Mock the Week, who was created by the same people as Whose Line, mixes this with a satirical Panel Show.
 * The night-time soap opera Knots Landing had an entire episode that was improvised by all the actors. The "script" for the episode merely gave the actors guidelines as to what should have happened by the time the episode was over, but in no way limited the actors on how they were supposed to accomplish their character's agenda.
 * In the US version of The Office, all the actors are given complete scripts, but are allowed to improvise as they go along. The absolute greatest adlib in the series is the kiss between Michael and Oscar, in Michael's failed attempt to show how tolerant he is of Oscar's homosexuality.


 * When auditioning for Cheers, John Ratzenberger originally read for the role of Norm. After badly botching his audition, he asked the producers if the show included a bar know-it-all, and proceeded to wander around the room ad-libbing lines that might be appropriate for such a character. A week later, he was called back and offered the newly-written role of Cliff.
 * Finishing recording the first ever episode of Peter Cook and Dudley Moore's Not Only but Also, the producer decided that since Dud was a pianist, they should record a play-out to go over the end credits. He had the credit roller set up, a grand piano placed in the middle of the set, and instructed Pete and Dud to say goodbye to the audience and then play until the credits ran out. Dud sat at the piano, Pete stood behind him, Dud struck a chord, sang a demi-falsetto "Now is the time to say goodbye..." and proceeded to compose their hit signature tune Goodbyeeee! on the spot.
 * The Janitor on Scrubs was not originally supposed to be a recurring character, so many of his scenes were improvised by Neil Flynn, which added to the Cloudcuckoolander behavior of the character. In many other instances the other actors would also improvise reaction lines and other moments.
 * At the end of most of the later episodes, you see earlier versions of some of the scenes where the dialogue gets progressively weirder/more inappropriate/just plain stupider until one of the actors breaks character and goes 'Oh, God, we can't use that!'
 * Green Wing
 * The Thick of It
 * In the german show "Shiller Street", everything is improved. Really: the actors knows only the beginning of the episode, and they receive instructions via headphones. It was so popular that it spawned similar shows in other countries.
 * When Neil Patrick Harris hosted the 2009 Tony Awards, he closed the ceremony by singing a song (to the tune of "Tonight" and "Luck Be a Lady"), the lyrics of which were just one variation based on the winners that had just been revealed that night. The lyricists (Mark Shaiman and Scott Wittman) had come up with lyrics for several possible winning scenarios, although they weren't prepared for certain scenarios like Billy Elliot winning Best Musical, but Elton John losing Best Original Score, and thus were tweaking the lyrics right up until the song went on. Neil Patrick Harris, being Crazy Awesome, pulled it off with aplomb, even throwing in an odd little bit of Painting the Fourth Wall halfway through ("Credits? That's not gonna stop me!").
 * Unlike many of today's tightly-scripted and -edited cooking programs, the original nationally-recognized cooking program, The French Chef with Julia Child (later known as Julia Child and Friends), was largely an improvised program, with the recipe and some of the mise en place just about the only already cemented elements of the program. If Julia made an error in the program, it stayed, and if she was having a problem with, say, butchering a piece of meat, that stayed too. Granted, this was pretty much the nature of many television programs at the time, but it added to Child's overall charm and likeability with the audience, because it gave the home cook the ability to see that everything didn't need to go perfectly. This arguably led to Julia Child's becoming the first celebrity chef and the progenitor of all the cooking shows on television today.
 * The regular troupe of The Carol Burnett Show would regularly go Off the Rails, and the resulting Throw It In featured the comedians failing to keep a straight face.
 * Charlie's rants in Its Always Sunny in Philadelphia were improvised on the spot. In later seasons he was paired more often with Dee because she was more able to roll with it without breaking on camera.
 * Parks and Recreation is shot on digital video rather than film to let the actors improvise at length without the high cost of film stock.
 * SaturdayMorningKidsShows are often only semi-scripted, because they're live and the kids are going to throw everything off anyway. SMTV Live interspersed scripted sketches (with lots of Throw It In and Lampshade Hanging of forgotten lines) with unscripted chat, while Dick and Dom In Da Bungalow was pretty much entirely Improv- Word of God is the hosts just had a running order, no script. A couple of actors played lots of recurring characters who would come in each week, and would have a few prepared jokes when they first entered, but they would then have to improvise as they interacted with the hosts and the children.
 * Community is fond of this.
 * Many guests on the Colgate Comedy Hour preferred this over following the script.

Music

 * Improvisation happens a lot in the music world, especially jazz. Improvisations in the world of jazz music are varied, depending on the subgenre. Swing musicians usually just "riffed" on the melody, while the bebop musicians played extended solos on the chord changes. Miles Davis edited hours of recordings of his musicians loose improvisations to create "Bitches Brew". Ornette Coleman pioneered free jazz, improvisation using no chord changes at all. And the genre continues...
 * Jazz musicians spend HOURS working on improvisation. John Coltrane and Charlie Parker were well-known for extremely long practice sessions, sometimes lasting up to 14 hours.
 * One of the landmarks in jazz improvisation came from saxophonist Coleman Hawkins's recording of Johnny Green's "Body and Soul" in 1939. Instead of playing the melody and then soloing, Hawkins stated the melody for about 4 bars and went on a long, intricate exploration of the chord changes for the rest of the verse and another one. Disliked by the general public at the time, Hawkins' solo is considered an evolutionary leap and a defining factor in modern jazz improvisation.
 * In baroque and classical concertos there is a section called a cadenza, where the soloist goes on an unaccompanied flight of fancy, before leading the orchestra in to finish the cadenza. It used to be customary to improvise these, but in modern times, cadenzas are almost always written out beforehand, and in romantic concertos, the composer often writes the cadenza as well.
 * Organists are expected to be able to improvise, and improvisation is a component of high-level exams in most conservatories.
 * Blues, rock and to a lesser degree Heavy Metal are some other genres that tend to feature a lot of instrumental improvisation. Like in jazz, improvisation in these genres is usually based on the "pentatonic blues scale".
 * George Gershwin found out about his being booked to write and perform a new piece for an upcoming concert only three weeks before the concert was supposed to go on. The score he turned in for "Rhapsody in Blue," which he'd composed in those three weeks, had blank spaces where his piano solos were supposed to go, with the notation "Wait For Nod" to tell the conductor when to bring the rest of the orchestra back in.
 * The Frogs' songs are often improvisation heavy, and sometimes this will include clearly flubbing a lyric, then quickly trying to find a way to make it still work, often while in character. One particularly obvious case of this is the following passage of "I'm Hungry": "You can't eat food with a bent throat! YOU try fooding eat - You eat... Yeah, you eat all right! I watch you eat! I never get no food...."
 * In the music video for New Found Glory's cover of "Kiss Me", one of the band members hands a kid with a cape his guitar during the solo. The kid, who was one of the many extras that were recruited to simply run around the set in a crazed manner, just happened to be right in front of the band at that instant and froze in confusion, so he was given the guitar in an improvised moment.
 * Ella Fitzgerald was performing "Mack the Knife" for her live Berlin album, but forgot all the words after the first verse. She quickly improvised new lines and a scat solo, keeping up perfectly with the rhythm section. The final cut was so good that she got a Grammy for it.
 * The acoustic guitar solo at the start of "And You and I" by Yes was an unplanned improv. They were gearing up to start recording the track, and Steve Howe was doodling and checking the tuning on his guitar. Jon Anderson thought it sounded "beautiful" and signalled to Eddie Offord to start recording. The whole thing made it into the album mix, including Eddie responding "OK" to Jon's signal after he starts the tape.
 * Gerry Rafferty's greatest hit "Baker Street" arguably owes its success to its distinctive sax break. This was improvised in its entirety by Raphael Ravenscroft, the session musician who had been hired to play sax on the album, City to City (and recorded in the wrong key).
 * The vocal on Pink Floyd's "The Great Gig in the Sky". It was originally planned and recorded as an instrumental track, but producer Alan Parsons thought it could do with something more, and suggested they get vocalist Clare Torry in for a vocals session. Roger Waters recalls the musical direction they gave her amounting to: "There's no lyrics. It's about dying — have a bit of a sing on that, girl." Clare had a listen through, and then overdubbed her vocals in one take. The entire vocal part was her own invention, improvised on the spot.
 * This actually caused quite a lot of fuss. As Torry was merely hired as a session singer she received the Union rate of a mere £30 in return for one of the most iconic moments on one of the best selling albums of all time. In 2004 and she sued, claiming that as she improvised the whole take with no help from the band, she effectively wrote her own part and deserved both a co-writing credit and a share of the royalties. The case was settled out of court a year later, and she was awarded an undisclosed sum and all subsequent releases of the track have given her a writing co-credit.

Radio

 * BBC radio show The Masterson Inheritance is improvised from a set of plot elements given by the audience. (It shares a few cast members with Whose Line...)
 * Central to the legend -- if not always the actual performance -- of comedy team Bob & Ray. Their act began literally as two guys batting it around on-air, and never stopped sounding like it, regardless of an increasing reliance on scripts as their performance workload got heavier.

Theatre

 * Formalised in Theatresports
 * The Complete Works of William Shakespeare  by the Reduced Shakespeare Company basically writes this into the script with places that essentially say "you improvise here", as well as numerous audience participation moments. Every performance has to invoke this trope.
 * Evelyn Evelyn: The "Ask Evelyn Evelyn" bit of the stage show. The sisters give their answers one word at a time, trying to form a full sentence by following up on each other's words... which mostly involves Amanda and Jason trying to think of words that the other could not possibly follow up on.
 * Many comedic theatre troupes are known for developing sketches from improvisation. Some of the prominent ones are:
 * Second City - Chicago, Toronto, other locations of varying permanence
 * The Groundlings - Los Angeles
 * UCB (Upright Citizens Brigade) Theatre - New York and LA, with roots in Chicago
 * Boom Chicago - Amsterdam, but mostly made up of Americans
 * Bad Dog Theatre Company - Toronto
 * Improv Asylum - Boston
 * The Comedy Store Players- London. Many of the early cast of Whose Line Is It Anyway, started off there, and the BBC radio show The Masterson Inheritance is basically one long Players sketch per episode.
 * Australian comedy team The Umbilical Brothers. A few of their routines are improvised, including suggestions from the audience.

Western Animation
"James Lipton: IMPROV!"
 * Most of the Constructicon's dialogue during their first appearance in Transformers Animated was ad libbed by their voice-actors, as was a lot of other things, including Blitzwing's German accent the entirety of The Stinger in the season two finale.
 * According to the Wiki, the entire final scene of "A Bridge Too Close" was improvised!
 * In Avatar: The Last Airbender, Sokka was supposed to be a more serious warrior character. However, the improvisation of his All That cast-member voice-actor lead to him becoming the Plucky Comic Relief.
 * On Family Guy when Chris (Seth Green) works at the Quahog mini-mart, the conversations about movies with his boss, Carl (Jon Benjamin) were improvised.
 * Note that all of Job Benjamin's own series' involve large amounts of improve, Dr. Kats, Home Movies, and more recently Archer.
 * And then there's the episode where Peter, Quagmire and Joe try to set up an improv group. It doesn't go well.


 * Parodied in The Simpsons, where an improv team is given "A Starbucks in Serbia" as their setting. "I'll have a coffee" "That'll cost $8. This is Starbucks!" (audience mildly amused) "... In Serbia!" (rocking laughter).
 * All the dialog from Home Movies was done this way to make it sound like 3 kids talking in real life. Even the scripts only had small notes on them and jokes to fall back on if the voice actors couldn't think of anything to say.
 * Paul Rugg's audition to provide the voice of Freakazoid went way, way off-script. Nearly all of it was then animated as part of the first episode, "Dance of Doom."
 * Some episodes were written with a Paul Harvey-type narrator. Paul Rugg, warming up his Paul Harvey impression, would say things like "smack me with a handle" or "I think there's a thuuuuuuumbtack under my fanny!" and, as before, was surprised to see it had been animated as part of the episode.
 * In The Emperors New Groove, Patrick Warburton improvised when Kronk hummed his own theme song when he was carrying Kuzco in the bag to the waterfall. Disney legal department had Patrick to sign all rights to the humming composition over to them.

Other

 * Improv Everywhere. One of the more famous demonstrations of improv, it's a (now huge) [ who get together and "cause scenes" (that are all perfectly legal), with interactions of shocked bystanders being completely improvised.
 * Literally every major city (at least, in America) usually has an improv comedy show. Second City has very much popularized the art that lead to wider exposure on Whose Line.

Web Original

 * Web Therapy: Almost all of it.
 * Happens often on the Adam The Alien YouTube channel, both with random You Tubers, and with the Tokens Improv group. Often involving improvised a capella music.