Rouben Zachary Mamoulian (October 8, 1897 – December 4, 1987) was an American film and theatre director.

Mamoulian was born in Tbilisi, Georgia (ruled at that time by imperial Russia), to an Armenian family. His mother Virginia (née Kalantarian) (1876–1972) was a director of the Armenian theatre, and his father Zachary Mamoulian (1866–1966) was a bank president. Mamoulian moved to England and started directing plays in London in 1922. He was brought to the United States the next year by Vladimir Rosing to teach at the Eastman School of Music and was involved in directing opera and theatre.

In 1925, Mamoulian was head of the School of Drama, where Martha Graham was working at the time. Among other performances, together they produced a short, two-color film titled The Flute of Krishna, featuring Eastman students. Mamoulian left Eastman shortly after and Graham chose to leave also, even though she was asked to stay. In 1930, Mamoulian became a naturalized citizen of the United States. Child star Jackie Cooper stated in his autobiography that Rouben Mamoulian was his uncle, and this fact helped establish Cooper's early movie career.

Mamoulian began his Broadway director career with a production of DuBose Heyward's Porgy, which opened on October 10, 1927. He directed Wings Over Europe from late 1928 to 1929. He directed the revival of Porgy in 1929 along with George Gershwin's operatic treatment Porgy and Bess, which opened on October 10, 1935. Mamoulian was also the first to stage such notable Broadway works as Oklahoma! (1943), Carousel (1945), and Lost in the Stars (1949).

He directed his first feature film in 1929, Applause, which was one of the early sound films. It was a landmark film owing to Mamoulian's innovative use of camera movement and sound, and these qualities were carried to his other films released in the 1930s. Dr. Jekyll and Mr. Hyde (1931) benefits from having been made before the Production Code came into full force, and is regularly considered the best version of Robert Louis Stevenson's tale. Queen Christina (1933) was the last film Greta Garbo made with John Gilbert, and it benefits from being made before the Production Code came into full force. The musical film Love Me Tonight was released in 1932.

He directed the first three-strip Technicolor film Becky Sharp (1935), based on Thackeray's Vanity Fair, as well as the 1937 musical High, Wide, and Handsome. His next two films earned him wide admiration, The Mark of Zorro (1940) and Blood and Sand (1941), both remakes of silent films. Blood and Sand, about bullfighting, was filmed in Technicolor, and used color schemes based on the work of Spanish artists such as Diego Velázquez and El Greco. His foray into screwball comedy in 1942 was a success with Rings on Her Fingers starring Henry Fonda and Gene Tierney.

Mamoulian's last completed musical film was Metro-Goldwyn-Mayer's 1957 film version of the Cole Porter musical Silk Stockings. This was one of Porter's less successful stage musicals and was based on the 1939 Ninotchka. The film Silk Stockings starred Fred Astaire and Cyd Charisse, with Janis Paige and Peter Lorre in supporting roles.

Mamoulian's film directing career came to an end when he was fired from two consecutive films: Porgy and Bess (1959) and Cleopatra (1963). He previously had been fired as director of Laura (1944). After directing the highly successful original stage productions of Oklahoma! and Carousel, he worked on only a few other theatrical productions, such as St. Louis Woman, which introduced Pearl Bailey to Broadway audiences.

He personally was recruited by Directors Guild of America (DGA) co-founder King Vidor in 1936 to help unionize fellow movie directors. Mamoulian's lifelong allegiance to the DGA, and more so his general unwillingness to compromise, contributed to his being targeted in the Hollywood blacklisting of the 1950s.

He died on December 4, 1987 at the Motion Picture & Television Country House and Hospital of natural causes at the age of 90 in Woodland Hills, California.

The critical appraisal Rouben Mamoulian by Tom Milne was published as Cinema One Series, no. 13 by Thames & Hudson, 1969.

The biography Mamoulian: Life on Stage and Screen by David Luhrssen was published in 2013 (University of Kentucky Press).