Mr. Smith Goes to Washington is a 1939 American political comedy-drama film directed by Frank Capra, starring Jean Arthur and James Stewart, and featuring Claude Rains and Edward Arnold. The film is about a naive, newly appointed United States senator who fights against government corruption, and was written by Sidney Buchman, based on Lewis R. Foster's unpublished story "The Gentleman from Montana". It was loosely based on the life of Montana US Senator Burton K. Wheeler, who underwent a similar experience when he was investigating the Warren Harding administration.

The film was controversial in the US when it was first released, with attacks from many politicians claiming that it brought Washington into disrepute, but it was very successful at both the domestic and international box offices, and it made Stewart a major star.

Mr. Smith Goes to Washington was nominated for eleven Academy Awards, including Best Picture, Best Director and Best Actor, winning Best Original Story. Considered to be one of the greatest films of all time, the film was selected by the Library of Congress as one of the first 25 films for preservation in the United States National Film Registry in 1989, for being "culturally, historically, or aesthetically significant".