Breaking the Fourth Wall/Theatre

Opera

 * In Sergei Prokofiev's Love For Three Oranges the action is frequently interrupted by a Greek Chorus (or rather, four or five separate Greek Choruses) of opera fans and stagehands. This on its own doesn't quite break the fourth wall. But when the stagehands decide to intervene in the plot by kidnapping the main villain, you've got to feel like some kind of line has been crossed. Relatively rare in that the fourth wall is broken from the OUTSIDE: rather than one of the characters in the play turning to address the audience, characters from the "audience" reach in and start mucking about in the play.

Other Theatre
""Mark me now; now will I raise the waters.""
 * Shakespeare's plays often use this in monologues.
 * A Midsummer Night's Dream deserves special mention for Puck's ending speech, which can be condensed into "We're sorry if you didn't like the play," and, essentially, a Shakespearean version of the MST3K Mantra.
 * It also deserves a secondary mention for the continuous breaking of the fourth (fifth?) wall in the Pyramus and Thisbe second. Frequently the action stops so Bottom can reply to the characters watching the play. Plus the prologues. Oh, the prologues.
 * And of course in Henry V where the opening monologue is an extended apologia for not showing the tremendous battles that are going on in-between the play's scenes. Made doubly strange because it was retained in both the Olivier and Branaugh films of the play, where they do show the battles.
 * Any time Iago opens his mouth he is likely to address the audience by the end of the speech.
 * One of Hamlet's many soliloquies (this one in Act II, scene ii) includes the lines "I have heard that guilty creatures sitting at a play/Have by the very cunning of the scene/Been struck so to the soul that presently/They have proclaimed their malefactions..." A great many productions have Hamlet break the fourth wall at this line and speak directly to the audience, for a darkly comedic effect.
 * Launcelot in The Merchant of Venice tells the audience to pay attention while he plays a prank on his dad:

""But that's all one, our play is done, And we'll strive to please you every day.""
 * Feste singing at the end of Twelfth Night:

"Jeff: "It's Susan's turkey burger from earlier. Shh. Don't tell her." Susan: "I can hear you, Jeff.""
 * The epilogue in As You Like It, in which Rosalind admits her nature as a guy who plays a girl who dresses as a guy (or a girl who plays a guy who plays a girl who dresses as a guy, in most modern performances), complains that the play was no good, and flirts, collectively, with everyone in the audience so that they'll "like as much of this play" as they possibly can.
 * The Narrator of Our Town doesn't so much break the fourth wall as completely ignore it. The rest of the cast is entirely unaware that they're in a play or that what's happening isn't real, but the Narrator talks to the audience throughout the entire show. In between narration, he inserts himself into the action by picking up different bit parts, such as the owner of the soda shop, and interacting with the characters as one of them.
 * A more subtle but no less important one appears in the second act when during the wedding of two of the characters, the bible that the minister (also played by the Narrator) uses is not actually a bible but is in fact a copy of the script.
 * Normal in Pantomime, and many other forms of audience participation theatre.
 * Subverted in plays like Moby Dick Rehearsed where the action is set on the stage of a theatre and the front few rows are kept empty so that the cast can use them as though they were in an empty theatre.
 * Not to mention plays that remove the fourth wall altogether and have the actors go out and bother the audience.
 * Or even just move through them (or out from amongst them).
 * In Rent, Maureen asks the audience to moo with her near the end of her protest.
 * In Title of Show during a blackout in a scene where Susan isn't supposed to hear Jeff's dialogue, she calls him out for eating her turkey burger.

""When we are waxing humorous, Please don't wane. The jokes are obscure, but numerous -- We'll explain.""
 * Hunter reads aloud a real online post as a revenge of sorts, "Dear Talkin' Broadway's 'All That Chat,' is it true [title of show] has its eye on Broadway? Why would anyone think a tiny, 'insidery' downtown show would appeal to a wider audience is beyond me. I'm sorry, but four chairs and a keyboard do not a musical make. That said, I wouldn't be surprised if their crappy show actually does get to Broadway and they just put this entire posting in it word for word. Signed, sweeneyluvr12."
 * Done all throughout N F Simpson's A Resounding Tinkle. At numerous points, the 'Author' comes on to explain to the audience about what is happening; characters discuss whether they should carry on entertaining the audience or just leave them to it, at one point a group of critics come on stage and discuss the play so far and the play ends when an audience member protests loudly about the quality of the show.
 * Smashed to ribbons in Spamalot when the Lady of the Lake explains to Arthur that he is in fact in a Broadway/West End Musical, and they go out into the audience to look for the Grail, which is found under a patron's chair.
 * And while the Lady of the Lake's actor interrupting the show with a song complaining about being part of this absurd show where the characters are looking for shubbery and she needs a better agent isn't technically Breaking the Fourth Wall, because she's playing herself, after she does get back in character she make a comment about the fact she hasn't been on stage for far too long, although she had a great lounge number in act 1. Which is strangely meta, because the actor has been on stage, in the aforementioned interrupting song, but the character hasn't.
 * Used for both humorous and chilling effect in the Stephen Sondheim musical The Frogs.
 * The humorous: The opening song, "Invocation and Instructions to the Audience":

""And a leader's useful to curse, And the state of things could be worse. And besides... It's only a play.""
 * The chilling: The god Dionysos has gone to the underworld to retrieve a great dead playwright whose new work can revitalise the public and save the world, but Pluto, king of the underworld, discourages him, and a chorus of the dead counsels inaction and apathy:

"What happened then? Well that's the play And he wouldn't want us to give it away Not Sweeney, not Sweeney Todd..."
 * This is directly from the original. Aristophanes' ancient Greek comedy, Frogs, opens with Dionysus' servant Xanthius asking (per the Paul Roche translation), "Hey, boss, like me to perk things up a bit with one of those corny cracks that always get the audience laughing?"
 * Aristophanes believed that the fourth wall existed to be broken. Clouds has the Anthropomorphic Personification of the right and wrong arguments arguing about stoicism. The right argument voices the opinion that if you're hedonistic your landlord will think you're gay. The wrong argument then defeats this by pointing out that most politicians are gay, most religious leaders and from the look of it most of the audience too.
 * In the musical Spring Awakening, whenever a singing number takes place, the actors on stage take out microphones they've been hiding in their pockets. Like in Chicago, the idea is that whenever they're singing they're imagining it's happening on a stage in front of an audience. As such, that actually is happening, but the characters don't actually know that.
 * The Complete Works Of Shakespeare Abridged has the actors frequently talk to the audience, and discuss the plays they are supposed to be performing with each other. At one point, audience members are even invited on stage to participate in a scene. The ones sitting in their seats aren't left out, either.
 * Complete Works doesn't so much break the fourth wall as shatter it with a sledgehammer, then gleefully dance on the pieces for an hour and a half.
 * "The Ballad of Sweeney Todd", which opens Sweeney Todd: The Demon Barber of Fleet Street, features a somewhat bizarre bit of fourth wall breaking, with the main character talking about himself in the third person:

"Scriptreader: i told you there was a prop director, I told you there was a writer, I'm narrating, Of course there's an Audience! come on, do you to even watch theater?"
 * The second act of Into the Woods features the main characters
 * Pretty much the whole point of Stephen Gregg's one-act S.P.A.R. (Stephen's Play About Renata) The author is summoned when the eponymous Renata holds a seance to find out about her crush Todd, and he proceeds to reveal the existence of the fourth wall. Renata literally puts her head through it and discovers the audience, and then the trope is further played out when three audience members are called to scrutinize a wall of the theater and reveal that there is another audience watching the audience. Finally, Stephen Gregg himself is called upon to scrutinize the wall, and discovers that  The whole play's a bit of a Mind Screw, unsurprisingly.
 * As the plot of Nunsense revolves around the nuns putting on a variety show to raise money, there is literally NO fourth wall, as it's assumed that the audience came to see them perform, as opposed to a play. As such, there's a lot of interaction with the audience beyond merely speaking to them, including interaction with the orchestra pit, dancing, and a quiz for the audience to see who was paying attention to the opening.
 * Absolutely shattered in Billy Twinkle: Requiem for A Golden Boy, when Billy jumps off the cruise ship prop, to find that he is on a stage, and asks Sid-the hand-puppet personification of his crotchety mentor-"Who are all these people?" to which Sid replies "They're your audience, you idiot!" Yes, It Makes Sense in Context . I swear.
 * In Avenue Q, the characters are struggling to raise enough money. Hence their decision to go pester people who clearly have enough money to waste on things like theatre shows. They then go into the audience looking for spare change.
 * The Glass Menagerie opens with one of the characters explaining to the audience that this is a play based on his memories. The script comes with very detailed instructions for how to make the play appear as if it's being told through memories, although they're not always followed.
 * Fiddler on the Roof's Tevye speaks to the audience quite often, either to explain why he and his family are like a fiddler on a roof or to battle with his principles when his daughters break various traditions.
 * This is used in A Very Potter Musical, when Ron enters and tells Harry that he'd been hanging out with Hagrid backstage.
 * "Now that we've got that four-part harmony out of the way, why don't we look for that horcrux?"
 * Some theatre adaptations of Terry Pratchett's Discworld preserve the humour in the footnotes with a character called "Footnote" who sounds a horn to freeze the action, comes on stage to say the note and sets things going again.
 * Done beautifully by Lonnie in Rock of Ages, in which he cheers up the main character by telling him that everything he has done thus far has happened within a broadway play.
 * Done in the final scene of Dog-Ear, when Ian and Ell discover the Scriptreader on the balcony.
 * and steal her script.. and promptly run off into the night.

"Madea: This is a play; ain't no room or no door up here!"
 * In the most recent London revival of Oliver!, Fagin breaks the fourth wall during a few of his monologues, especially when he is play acting with his 'treasures'. For example, he was looking through an opera glass and pretending he was at a theatre, gesturing towards the Stalls in the actual theatre (where the most expensive seats are) and mentioning that was where all the rich people were, then gesturing at the top tier and saying that was full of poor people. In the second monologue he started recounting the story of the musical and ended up saying: "What the Dickens am I going on about?"
 * In the live-action play version of the Tyler Perry film I Can Do Bad All By Myself, Perry's character Madea is asked to leave the living room so a private conversation can be had. A couple minutes later she makes a comment and is asked why she didn't go to her room. Her response?

"Montague: Excuse me, but what are you doing? Prince: Just talking to them. Montague: My fourth wall? Why do you call it “them?” Prince: What do you mean your “fourth wall?” Montague: These are my first three walls, and that one is the fourth. Benvolio: Which is wall number one? Montague: I don’t know. I just know this one is the fourth wall."
 * Due to Peter Pan being the Trope Namer for Clap Your Hands If You Believe, the theater production of course does this. After Tinkerbell takes poison that was meant for Peter, he looks out into the audience and asks them if they believe in fairies. Then he tells them to clap their hands if they do believe in fairies in order to save Tinkerbell.
 * In the musical adaptation of Vanities, the cast don makeup, wigs, and costumes for each of the four scenes at on-stage vanity tables. The first scene uses Audience Participation for a cheer. In the Theatre Works Palo Alto world premiere, Mary addressed the audience during the Set-Switch Song "Open Up Your Mind".
 * In the Screen to Stage Adaptation of High School Musical 2, Sharpay asks the actual orchestra drummer to "play her a beat".
 * In The Prisoner of Second Avenue, Mel literally breaks one of the set walls by banging on it too hard, and the crew repair it (and the rest of the apartment) during the intermission. During scene transitions, a circle of television sets drops down and displays a Channel 6 news report to the audience.
 * At the climax of "The Lambeth Walk" from Me & My Girl, the company dances through the aisles.
 * In Assassins, during the song "How I Saved Roosevelt," Giuseppe Zangara yells at the audience for laughing at one of his lines.
 * In Romeo and Juliets Unofficial, Unnecessary Sequel Prince Escalus acts as the narrator, routinely talking directly to the audience. At one point he is caught doing this by Lord Montague, resulting in the following exchange:


 * In the Screen to Stage Adaptation of Aladdin, Babkak, Omar, and Kassim frequently do this, such as commenting on prop camels and split scenes, as does the Genie during the "Friend Like Me" number.
 * Done wonderfully in Hair (theatre). The actors run through the audience, hand out flyers and flowers, and ask for spare change. At one point, Claude even says "Mother, the audience!"
 * The opera Gianni Schicchi ends with the title character turning to the audience and imploring them to clap their hands if they believe he deserves a better fate than what he got according to Dante (whose Divine Comedy found him in the eighth circle of hell). He starts the applause himself.
 * In ACT Theatre's annual play of A Christmas Carol, the Ghost of Christmas Present sprinkles his torch incense on the front row of the audience. In the opening scene, the cast members greet various audience members with "Merry Christmas".
 * A Funny Thing Happened on the Way to the Forum opens and closes with the song "Comedy Tonight", in which the actors directly address the audience, telling about the show they're about to see (or have just finished seeing).
 * In the recently premiered musical First Date, each of the characters addresses the audience during the opening song.
 * In the final Seattle run of Modern Luv, several references were made to the then-forthcoming New York run of the show. Also, the closing number dims the lights and has the audience hold up their cellphones/smartphones, as the songs lyrics say.
 * Fellowship! The Musical enjoyed doing this a handful of times - notably, once when Frodo tells Gandalf, "you scared me down-stage left!", and the Balrog scene, in which one character yells that they need to find an exit quickly, and another character points out the Exit sign for the theater's side exit, which they then leave out of.
 * In Tom Stoppard's play, Rosencrantz and Guildenstern Are Dead, some characters (namely Rosencrantz) will look at, gesture towards, or refer to the audience. Although they do not speak to the audience directly, they do talk about them.
 * Occasionally, a production of The Mikado will have the Lord High Executioner sing (in The List song), something akin to "There's the orchestra conductor who just now has lost his place." It substitutes for a line that is (almost) invariably changed due to Unfortunate Implications in the original.