One Flew Over the Cuckoo's Nest is a 1975 American psychological comedy drama film directed by Miloš Forman, based on the 1962 novel of the same name by Ken Kesey. The film stars Jack Nicholson who plays a new patient at a mental institution alongside Louise Fletcher who plays an austere nurse. It also features a supporting cast of Will Sampson, Danny DeVito, Sydney Lassick, William Redfield, as well as Christopher Lloyd and Brad Dourif in their film debuts.

Filming began in January 1975 and lasted three months, taking place on location in Salem, Oregon, and the surrounding area, as well as Depoe Bay on the north Oregon coast. The producers decided to shoot the film in the Oregon State Hospital, an actual mental hospital, as this was also the setting of the novel. The hospital is still in operation (as of 2022), though the original buildings seen in the film have been demolished. The film released on November 19, 1975. Considered by many to be one of the greatest films ever made, One Flew Over the Cuckoo's Nest is No. 33 on the American Film Institute's 100 Years... 100 Movies list.

The film was the second to win all five major Academy Awards (Best Picture, Actor in Lead Role, Actress in Lead Role, Director, and Screenplay) following It Happened One Night in 1934, an accomplishment not repeated until 1991 with The Silence of the Lambs. It also won numerous Golden Globe and BAFTA Awards. In 1993, the film was deemed "culturally, historically, or aesthetically significant" by the United States Library of Congress, and selected for preservation in the National Film Registry.