The Apartment is a 1960 American romantic comedy-drama film directed and produced by Billy Wilder from a screenplay he co-wrote with I. A. L. Diamond. It stars Jack Lemmon, Shirley MacLaine, Fred MacMurray, Ray Walston, Jack Kruschen, David Lewis, Willard Waterman, David White, Hope Holiday, and Edie Adams.

The film follows an insurance clerk (Lemmon) who, in hopes of climbing the corporate ladder, allows his superiors to use his Upper West Side apartment to conduct their extramarital affairs. He becomes attracted to an elevator operator (MacLaine) in his office building, unaware that she is having an affair with the head of personnel (MacMurray).

The Apartment was distributed by United Artists to widespread critical acclaim and was a commercial success, despite controversy owing to its subject matter. It became the 8th highest-grossing film of 1960. At the 33rd Academy Awards, the film was nominated for ten awards and won five, including Best Picture, Best Director, and Best Screenplay. Lemmon, MacLaine, and Kruschen were nominated for Best Actor, Best Actress, and Best Supporting Actor respectively, and Lemmon and MacLaine won Golden Globe Awards for their performances. Promises, Promises, a 1968 Broadway musical by Burt Bacharach, Hal David, and Neil Simon, was based on the film.

The Apartment has come to be regarded as one of the greatest films ever made, appearing in lists by the American Film Institute and Sight and Sound magazine. In 1994, it was one of 25 films selected for inclusion to the Library of Congress National Film Registry.