Once Upon a Time in America (Italian: C'era una volta in America) is a 1984 epic crime film co-written and directed by Italian filmmaker Sergio Leone, and starring Robert De Niro and James Woods. The film is an Italian–American venture produced by The Ladd Company, Embassy International Pictures, PSO Enterprises and Rafran Cinematografica, and distributed by Warner Bros. Based on Harry Grey's novel The Hoods, it chronicles the lives of best friends David "Noodles" Aaronson and Maximilian "Max" Bercovicz as they lead a group of Jewish ghetto youths who rise to prominence as Jewish gangsters in New York City's world of organized crime. The film explores themes of childhood friendships, love, lust, greed, betrayal, loss, and broken relationships, together with the rise of mobsters in American society.

It was the final film directed by Leone before his death five years later, and the first feature film he had directed in 13 years. It is also the third installment of Leone's Once Upon a Time Trilogy, which includes Once Upon a Time in the West (1968) and Duck, You Sucker! (1971). The cinematography was by Tonino Delli Colli, and the film score by Ennio Morricone. Leone originally envisaged two three-hour films, then a single 269-minute (4 hours and 29 minutes) version, but was convinced by distributors to shorten it to 229 minutes (3 hours and 49 minutes). The American distributors, The Ladd Company, further shortened it to 139 minutes (2 hours and 19 minutes), and rearranged the scenes into chronological order, without Leone's involvement.

The US edit was a critical and commercial flop in the United States, and critics who had seen both versions harshly condemned the changes made. The original "European cut" has remained a critical favourite and frequently appears in lists of the greatest films of all time, especially in the gangster genre.