Duck Soup is a 1933 American pre-Code musical comedy film written by Bert Kalmar and Harry Ruby (with additional dialogue by Arthur Sheekman and Nat Perrin) and directed by Leo McCarey. Released by Paramount Pictures on November 17, 1933, it stars the four Marx Brothers (Groucho, Harpo, Chico, and Zeppo in his final film appearance) and also features Margaret Dumont, Louis Calhern, Raquel Torres and Edgar Kennedy. Duck Soup was the last of the five Marx Brothers films released by Paramount Pictures. In the film, Groucho portrays Rufus T. Firefly, the newly installed president of the fictional country of Freedonia. Zeppo is his secretary, while Chico and Harpo are spies for the neighboring country of Sylvania. Relations between Firefly and the Sylvanian ambassador (Calhern) deteriorate during the film, eventually leading the two countries to war.

Compared to the Marx Brothers' previous films, Duck Soup was a financial disappointment, though not an outright box-office failure as is sometimes reported. The film opened to mixed reviews, although this by itself did not end the group's association with Paramount. Bitter contract disputes, including a threat by the Marxes to leave and found their own production company, soured their negotiations with the studio just as Duck Soup went into production. After the film fulfilled their contractual obligations to Paramount, the Marxes and the studio agreed to part ways.

While contemporaneous critics of Duck Soup felt it did not quite rise to the level of its predecessors, critical and popular opinion has evolved and the film has since achieved the status of a classic. Duck Soup is now widely considered to be a masterpiece of comedy and the Marx Brothers' finest film.

In 1990, the United States Library of Congress deemed Duck Soup "culturally, historically, or aesthetically significant" and selected it for preservation in the National Film Registry.