The film stars Glen Hansard and Markéta Irglová as two struggling musicians in Dublin, Ireland.

It was a commercial success, earning substantial per-screen box office averages in the United States, and received acclaim from critics.

He invites her to his father's shop, and on the bus home musically answers Girl's question about what his songs are about: a long-time girlfriend who cheated on him, then left ("Broken Hearted Hoover Fixer Sucker Guy").

At the shop, Guy introduces Girl to his father and takes her to his room, but when he asks her to stay the night, she gets upset and leaves.

Girl writes the lyrics for one of Guy's songs ("If You Want Me"), singing to herself while walking down the street; at a party, people perform impromptu (including "Gold").

On a break in the early morning, Girl finds a piano in an empty studio and plays Guy one of her own compositions ("The Hill").

Before leaving for the airport, Guy buys Girl a piano and makes arrangements for its delivery, then calls his ex-girlfriend, who is happy about his imminent arrival.

[6] Director Carney, former bassist for Hansard's band the Frames, had asked a long-time friend to share busker anecdotes and compose songs for the film, but originally intended the male lead to be played by actor Cillian Murphy,[7] who was an almost-signed rock musician before turning to acting.

Murphy also believed he did not have the vocal capabilities to belt out Hansard's octave-leaping songs, so he pulled out, as did the film's other producers, also withdrawing their financial support.

[9] Carney then turned to songwriter Hansard, who had done only one acting job before, a supporting role as guitarist Outspan Foster in the 1991 ensemble film The Commitments, the story of a Dublin soul music cover band.

Initially, Hansard was reluctant, fearing that he wouldn't be able to pull it off, but after stipulating that he had to be fully involved in the filmmaking process and that it be low-budget and intimate, he agreed.

[9] Produced on a shoestring, about 75 percent of the budget was funded by Bord Scannán na hÉireann (The Irish Film Board), with Carney committing some of his own money.

The Dublin street scenes were recorded without permits, and with a long lens so that many passersby didn't realize that a film was being made.

After its second weekend in release in the United States and Canada, the film topped the 23 May 2007 indieWIRE box office chart with nearly $31,000 average per location.

When informed of Spielberg's comments, director John Carney told Sky News, "in the end of the day, he's just a guy with a beard."

[27] The nomination's eligibility for the Oscar was initially questioned,[28] as versions of the song had been recorded on The Cost and The Swell Season albums and it was also included in the movie Beauty in Trouble (all released in 2006); those issues were resolved before the voting for the award took place.

Upon its March 2007 release in Ireland, RTÉ's Caroline Hennessy gave the film 4 out of 5 stars and termed it "an unexpected treasure".

"[35] Michael Dwyer of The Irish Times gave the film the same rating, calling it "irresistibly appealing" and noting that "Carney makes the point – without ever labouring it – that his protagonists are living in a changing city where the economic boom has passed them by.

"[36] On Metacritic, the film has a weighted average score of 88 out of 100 based on reviews from 33 critics, indicating "universal acclaim".

[39] In late 2007, Amy Simmons of Time Out London wrote, "Carney’s highly charged, urban mise-en-scène with its blinking street lamps, vacant shops and dishevelled bed-sits provides ample poetic backdrop for the film’s lengthy tracking shots, epitomised in a sequence where the Girl walks to the corner shop in pyjamas and slippers while listening to one of the Guy’s songs on her personal stereo.

With outstanding performances from Hansard and newcomer Irglová, Carney has created a sublime, visual album of unassuming and self-assured eloquence.

"[40] The Telegraph's Sukhdev Sandhu said, "Not since Before Sunset has a romantic film managed to be as touching, funny or as hard to forget as Once.

A collector's edition of the soundtrack was released on 4 December 2007 in the U.S. with additional songs and a bonus DVD featuring live performances and interviews about the film.

"All the Way Down" first appeared on the self-titled album from musician collective The Cake Sale, with Gemma Hayes providing vocals.

[55] Directed by John Tiffany, the cast features Steve Kazee as Guy and Cristin Milioti as Girl with sets and costumes by Bob Crowley.