''Once'' is a low-budget Irish movie about two musicians (Glen Hansard of The Frames and collaborator Markéta Irglová) who meet by chance and develop a relationship while writing and recording songs together. The film was made for €130,000 ($160,000 USD) and received significant critical acclaim for both its understated romance and for its music (no surprise, since Hansard and Irglová are professional musicians, not actors). The song "Falling Slowly" won the AcademyAward for Best Song.

Almost missed its Oscar due to the fact that parts of the soundtrack, including the winning song, were released on other albums by the same artists prior to the film being released. It was decided to give them their nomination (and inevitable award) anyway since though it technically broke the rules, the film had been in the can over two years by the time it was released, and Oscar glory had been completely outside their expectations. But let it be understood on no uncertain terms, this was far and away the favorite song of the year.

At 19, Irglová is the youngest person ever to win the Best Song Oscar.

Before, during and after the release of the movie Hansard and Irglova have performed as The Swell Season and have released two albums under that name, 2006's ''The Swell Season'' (containing many of the songs in ''Once'' recorded during the long time it took to get the film made) and 2009's ''Strict Joy'' (featuring songs about the end of Hansard and Irglova's real romantic relationship). Both were extremely critically acclaimed upon release.

The film was adapted into a [[TheMusical stage musical]] in early 2012, and holds the distinction of being the first musical ever to have a Broadway run scheduled before it had even opened Off-Broadway. The show opened on March 18 to fantastic reviews, with most critics praising it for keeping to the spirit of the film while making the proper changes to make it work on-stage. It won eight Tony Awards out of eleven nominations, including Best Actor In A Leading Role (Steve Kazee), Best Book, and Best Musical. A US Touring production was announced and the show opened in Dublin, and later, the West End in 2013.

!!This film provides examples of:
* BilingualBonus: That understated romance between Guy and Girl is never really resolved unless you know Czech. [[spoiler:If you do, then you can understand what Guy couldn't when Girl answered "No, I love you."]]
* [[spoiler:BittersweetEnding: Because the Guy DidNotGetTheGirl]].
* BoyMeetsGirl
* TheCastShowoff: Not just singing, but also composing. Nearly all of the songs were composed by the two stars. Hansard wrote 7 of the songs (8 if you count "Broken Hearted Hoover Fixer Sucker Guy"), Irglova wrote two, and two Hansard and Irglova composed together. "Falling Slowly" is the only song they both composed together and sang together in the film.
** The lead singer of "Gold" in this film is also its composer, Fergus O'Farrell.
* [[spoiler: DidNotGetTheGirl: Contrary to what is expected of quirky romances, Girl remains faithful to her estranged husband (who returns by the end of the film), and Guy leaves on a jet plane to win back his ex-girlfriend]].
* DuetBonding
* EarnYourHappyEnding: Though mileage may vary on how bitter, or how sweet, the ending is, [[spoiler: by the time the film is over both Guy and Girl have found strength to move on from past heartbreak and give love a second chance, and Guy's music career is off to a pretty good start.]]
* EnforcedMethodActing: The scene when Girl tells Guy [[spoiler: "I love you" in unsubtitled Czech]] was ad-libbed. Guy's look of confusion is genuine.
** The opening chase scene also qualifies; they shot without permits, so when the heroin addict runs off with Guy's money, a pedestrian wound up injuring the actor by trying to stop what he thought was an actual robbery.
* ManicPixieDreamGirl: Downplayed. Girl is certainly enthusiastic, but direct and practical rather than aimless and quirky. Furthermore, she has baggage of her own, and can't magically help Guy put his life back together. But Guy is grateful to her nonetheless, and he tries to pay back for the courage she gave him.
* MayDecemberRomance: At the time of filming, Hansard was twice Irglová's age.
* MeetCute
-->'''Guy''': [[DeadpanSnarker "Ten cents! That's brilliant! Thanks!"]]
* UsefulNotes/TheNewIrish: Girl is a Czech immigrant in Dublin, no doubt to take advantage of the freedom of movement and labor after the Czech Republic joined the EU in 2004.
* NoNameGiven: Neither of the two main characters is ever referred to by name, and they're credited as "Guy" and "Girl." Guy's dad, Guy's girlfriend, Girl's [[spoiler:husband]] and Girl's mother are also unnamed.
** The silent video footage of the girlfriend is actually of writer/director John Carney's real life girlfriend, most of it (the parts that don't feature Hansard) was originally just amateur footage Carney shot of her before he even thought of making Once. At one point she says something to the camera and lip-reading reveals she's saying, [[spoiler:"Stop it, Johnny."]] Carney and Hansard point this out in the DVD audio commentary and joke that you now know the Guy's first name.
* [[spoiler:RaceForYourLove: Guy searches for Girl before he leaves for his flight to say his goodbyes, but ultimately cannot find her. Instead, he sends her a piano, which is what she has always wanted]].
* RealityIsUnrealistic: Of the mistaking-fiction-for-reality variety. Because the 2 stars are 1) not professional actors, 2) are music performers/composers (like their characters), 3) composed all the songs (again, like the characters), and 4) are playing characters with NoNameGiven, many people thought this was some kind of documentary about what actually happened to Hansard and Irglova.
** The enraptured reactions of audience characters to the Guy's music can also be a little hard to take seriously. [[SmallNameBigEgo It's not like the stuff won an Oscar or anything]]. [[HilariousInHindsight Oh wait.]]
* RealitySubtext / RomanceOnTheSet: Hansard and Irglová were indeed [[IncrediblyLamePun falling slowly]].
** They didn't last as a couple. They broke up in 2008 while touring as The Swell Season, although they remain friends. Their 2009 album ''Strict Joy'' is about the end of their romantic relationship.
* {{Scatting}}: The first time Guy leads the Girl through "Falling Slowly," he does so by just going "Ba, ba, ba ba..." It becomes quite funny when his voice cracks at the high note. But when he actually sings, [[SingingVoiceDissonance the entire song falls into place.]]
* SerenadeYourLover: Subverted. When they're alone with a piano, the Girl sings a love song to the Guy... [[spoiler: but it's a heartbroken ode to the husband she left, and she can't even bring herself to finish it.]]
* ShownTheirWork: The film showcases Glen Hansard's knowledge of the minutiae of busking, such as cover versions earning far more than original songs.
* SpiritualSequel: in ''TheCommitments'', Glen Hansard plays Outspan and finishes the film busking on the streets of Dublin. Cut forward twenty years and Glen Hansard stars in film which opens with his character... busking on the streets of Dublin. Bonus points due the fact that his character in ''Once'' isn't named.
* ThrowItIn: "Broken-Hearted Hoover-Fixer Sucker Guy" was just Glen Hansard goofing off between takes. Much to his surprise, it wound up in the final cut -- and the soundtrack.
** Irglová's line, where she says [[spoiler:"No, I love you,"]] in Czech, was also an ad-lib, and Hansard's look of confusion is genuine.
* UncommonTime:
** "Gold" is primarily in 6/8 and 4/4, but throws in some other half-measures for the heck of it. It also has a habit of taking the 4/4 bars as 3+3+2/8, making it sound like 6/8 - 6/8 - 2/4.
** Next to that, "When Your Mind's Made Up" being in 5/4 looks positively straightforward.
* WhatMightHaveBeen: Creator/CillianMurphy was originally slated to play the Guy and the Girl was supposed to be a little older than him. But John Carney had trouble finding an Eastern European singer/actress of the right age, so Glen Hansard (hired to provide the songs and anecdotes on being a busker) suggested Irglova (whom he was just starting to collaborate with). But when she was cast, Murphy backed out of co-starring with an unknown non-actor, so in desperation, Carney asked Hansard to play the Guy.

!!The Broadway musical contains examples of
* AdaptationExpansion: There are some new characters added and others have their roles expanded. For instance, the banker from the film who approves the loan due to his own love of music plays cello for the group's band.
* BookEnds: "Falling Slowly" is the first complete number of the show, and also the last. (It is preceded by "Leave," but the Guy falls apart mid-performance and isn't able to continue.)
* TheCastShowOff: To an even greater extent than the movie, because ''there is no orchestra''. Every actor also plays backing instruments. Sometimes they even do it in-character.
* DiegeticMusic: a fair bit of it is, despite being a musical.
* DreadfulMusician: the banker. His guitar playing is serviceable, but...
-->'''Girl:''' Don't sing.\\
'''Guy:''' Ever.
* TheGhost: the Girl's husband never appears, though he is the topic of some discussion.
* GreekChorus: actors who aren't currently playing named characters (or characters with an identity, given that the male and female leads don't have names) take on this role in the meantime.
* ManicPixieDreamGirl: The Girl, probably due to the fact that it would be tough to make the painfully shy characterization from the film work well on stage.
* NotableOriginalMusic: Hansard and Irglova composed and arranged a couple new songs for the musical, including the Czech folk tune "Ej Pada Pada Rosicka" and the new Guy solo "Sleeping".
* RunningGag: "I'm always serious. I'm Czech."
* ScreenToStageAdaptation: winning a bunch of awards, providing the setting to one of Creator/NeilPatrickHarris's [[http://www.youtube.com/watch?v=danBaPWT09A Tony Award]] openers, and bringing the original Girl, Cristin Milioti, to the eyes of the ''Series/HowIMetYourMother'' casting directors.
* StraightGay: The banker off-handedly reveals that he's "more of a penis person" in response to Billy's enthusiastic retelling of his [[note]]first ever[[/note]] sexual experience (with Réza) the night before. Billy doesn't get it, at first.
--> '''Billy:''' Well, you'd have a hard time finding one on a woman, wouldn't you? ''[Beat]'' [[DelayedReaction Oh, understood]].
* TactfulTranslation: Babushka tells a long, fanciful story about a man who dreamed and feared and shat in his bed. Her daughter merely translates this as, "Good luck."
* TranslationConvention: When Czech characters talk privately, they speak English while Czech subtitles are projected above the stage. This later becomes a ChekhovsGun during the BilingualBonus scene mentioned above, where when she says [[spoiler:I love you]] to Guy in Czech, it is subtitled in English.