A Funny Thing Happened on the Way to the Forum is a 1966 period musical comedy film directed by Richard Lester, based on the stage musical of the same name with music and lyrics by Stephen Sondheim, and book by Burt Shevelove and Larry Gelbart. It stars Zero Mostel and Jack Gilford, reprising their roles from the Broadway stage production. It also features Buster Keaton in his final screen role; Phil Silvers, for whom the stage musical was originally intended; and regular Lester collaborators Michael Crawford, Michael Hordern, and Roy Kinnear.

The film was adapted for the screen by Melvin Frank and Michael Pertwee. The story is inspired by the farces of the ancient Roman playwright Plautus (251–183 BC) – specifically Pseudolus, Miles Gloriosus, and Mostellaria – and tells the bawdy story of a slave named Pseudolus (Mostel) and his attempts to win his freedom by helping his young master woo the girl next door.

The film was released by United Artists on October 16, 1966, and was a critical and commercial success. It was nominated for Best Motion Picture – Musical or Comedy at the 24th Golden Globe Awards, while Ken Thorne won an Oscar for Best Music, Scoring of Music, Adaptation or Treatment.