Witness for the Prosecution is a 1957 American legal mystery thriller film directed by Billy Wilder and starring Tyrone Power, Marlene Dietrich, and Charles Laughton, with Elsa Lanchester and John Williams. The film, which has elements of bleak black comedy and film noir, is a courtroom drama set in the Old Bailey in London and is based on the 1953 play of the same title by Agatha Christie. The first film adaptation of Christie's story, Witness for the Prosecution was written for the screen by Wilder and Harry Kurnitz and adapted by Larry Marcus.

The film was acclaimed by critics and received six Academy Award nominations, including Best Picture. It also received five Golden Globe Award nominations including a win for Elsa Lanchester as Best Actress in a Supporting Role. Additionally, the film was selected as the sixth-best courtroom drama ever by the American Film Institute for their AFI's 10 Top 10 list.

In the film, a man accused of killing a wealthy widow who had named him as the main beneficiary in her will undergoes a trial during which his wife testifies against him.