''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 UsefulNotes/AcademyAward for Best Song.

It almost missed its Oscar because 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."]]
* BittersweetEnding: [[spoiler:Because the Guy DidNotGetTheGirl]].
* BoyMeetsGirl
* DidNotGetTheGirl: [[spoiler: 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.]]
* 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.
* MeetCute
-->'''Guy''': [[DeadpanSnarker "Ten cents! That's brilliant! Thanks!"]]
* 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.
* RaceForYourLove: [[spoiler: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.[[note]]There eventually would be a documentary about Hansard and Irglová and their post-''Once'' lives, 2011's ''The Swell Season''.[[/note]]
** 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.]]
* {{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.]]
* SecondLove: When the Guy and the Girl meet, he's still in anguish over his longtime girlfriend who cheated on and dumped him; she's conflicted over having left her husband. [[spoiler: Subverted at the end. They give each other the strength to seek closure or a new beginning with their ''first'' loves.]]
* 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 ''Film/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.
* 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.

!!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 specific characters take on this role in the meantime.
* ManicPixieDreamGirl: The Girl, probably because 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."
* TeasingFromBehindTheLanguageBarrier: When the Guy asks the Girl whether she still loves her husband, she replies in Czech: "I love you", but coyly refuses to translate it.
* 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.