The Lady Vanishes is a 1938 British mystery thriller film directed by Alfred Hitchcock, starring Margaret Lockwood and Michael Redgrave. Written by Sidney Gilliat and Frank Launder, based on the 1936 novel The Wheel Spins by Ethel Lina White, the film is about an English tourist travelling by train in continental Europe who discovers that her elderly travelling companion seems to have disappeared from the train. After her fellow passengers deny ever having seen the elderly lady, the young woman is helped by a young musicologist, the two proceeding to search the train for clues to the old lady's disappearance.

The Lady Vanishes was filmed at the Gainsborough Studios in Islington, London. Hitchcock caught Hollywood's attention with the film and moved to Hollywood soon after its release. Although the director's three previous efforts had done poorly at the box office, The Lady Vanishes was widely successful, and confirmed American producer David O. Selznick's belief that Hitchcock indeed had a future in Hollywood cinema.

The British Film Institute ranked The Lady Vanishes the 35th best British film of the 20th century. In 2017, a poll of 150 actors, directors, writers, producers and critics for Time Out magazine saw it ranked the 31st best British film ever. It is one of Hitchcock's most renowned British films, and the first of three screen versions of White's novel as of January 2021.