Once Upon a Time in America is a 1984 Jewish-American epic crime film co-written and directed by Sergio Leone and starring Robert De Niro and James Woods. The story chronicles the lives of Jewish ghetto youths who rise to prominence in New York City's world of organized crime. The film explores themes of childhood friendships, love, lust, greed, betrayal, loss, broken relationships, and the rise of mobsters in American society.

Leone adapted the story from the novel The Hoods, written by Harry Grey, while filming Once Upon a Time in the West. From there, Leone began production of Once Upon a Time in America. The film went through various casting developments and production issues before filming began in 1982.

The original version by the director was 269 minutes (4 hours and 29 minutes) long, but when the film premiered out of competition at the 1984 Cannes Film Festival, Leone had cut it down to 229 minutes (3 hours and 49 minutes) to appease the distributors. This was the version that was to be shown in European cinemas. However, for the US release on June 1, 1984, Once Upon a Time in America was edited down even further to 139 minutes (2 hours and 19 minutes) by the studio and against the director's wishes. In this short version, the flashback narrative was also changed, by moving the scenes in chronological order. Leone was reportedly heartbroken by the American cut, and never made another film before his death in 1989, making this his final film.

In March 2011 it was announced that original 269 minutes version was to be re-created by a film lab in Italy under the supervision of Leone's children, who have acquired the Italian distribution rights, and the film's original sound editor, Fausto Ancillai, for a premiere in 2012 at either the Cannes Film Festival or the Venice Film Festival.