Forty Thieves or 40 Thieves most often refers to the characters in the story of Ali Baba and the Forty Thieves.
It may also refer to:
Groups of people Forty Thieves (New York gang), an 18th-century New York street gang Forty Thieves (New York City Common Council 1852–1853) Forty Elephants, also known as the Forty Thieves, an all-female London criminal gang specializing in shoplifting The nickname for the participants in the 1921 Cairo Conference
Theatre, film and television The Forty Thieves, an 1878 British pantomime version of the Ali Baba story The Forty Thieves (1869 play), a burlesque performed on Broadway Forty Thieves (film), a 1944 Hopalong Cassidy Western
Other uses Forty Thieves (card game), another name for the solitaire game Napoleon at St Helena Vengeur-class ships of the line, whose notoriously poor construction caused them to become known as the "forty thieves." "40 Thieves" (A Loss for Words song)