The Naughty Nineties is a 1945 American film starring the comedy team of Abbott and Costello. The film is noteworthy for containing a filmed version of the duo's famous "Who's on First?" routine. This version is shown at the National Baseball Hall of Fame and Museum in Cooperstown, New York.

Abbott and Costello were an American comedy duo composed of comedians Bud Abbott and Lou Costello, whose work in radio, film, and television made them the most popular comedy team of the 1940s and 1950s, and the highest-paid entertainers in the world during the Second World War. Their patter routine "Who's on First?" is considered one of the greatest comedy routines of all time, a version of which appears in their 1945 film The Naughty Nineties.