What's My Line? is a panel game show that originally ran in the United States, between 1950 and 1967, on CBS, originally in black and white and later in color, with subsequent U.S. revivals. The game uses celebrity panelists to question contestants in order to determine their occupation. The majority of the contestants were from the general public, but there was one weekly celebrity "mystery guest" for whom the panelists were blindfolded. It is on the list of longest-running U.S. primetime network television game-shows. Originally moderated by John Charles Daly and most frequently with regular panelists Dorothy Kilgallen, Arlene Francis, and Bennett Cerf, What's My Line? won three Emmy Awards for "Best Quiz or Audience Participation Show" in 1952, 1953, and 1958 and the Golden Globe Awards for Best TV Show in 1962.

More than 700 episodes exist as kinescope recordings, filmed in 16mm, which was the only way moving pictures and sound from spontaneous, unscripted television shows could be preserved on a long-term basis prior to the emergence and subsequent widespread use of videotape. Many early episodes were lost because of economic decisions made by CBS executives between 1950 and 1952. Every episode from July 1952 to September 1967 existed for a long time in the archive of producers Mark Goodson and Bill Todman, but some of the episodes were lost in 1975.

After the Sunday night series's cancellation by CBS in 1967, it returned in a syndication package for local television stations that committed to airing it five days a week. This version originally was hosted by Wally Bruner and later by Larry Blyden. It was seen by viewers from 1968 to 1975. There have been a dozen international versions, radio versions, and a live stage version. Revivals in the U.S. were proposed several times, but all of them failed to go past the planning stages. New episodes have not been created for American television since December 12, 1974.

In 2013, TV Guide ranked What's My Line? ninth on its list of the 60 greatest game shows ever and Time ranked it as one of the 100 "All-Time" TV shows ever.