Union Pacific is a 1939 American Western drama directed by Cecil B. DeMille and starring Barbara Stanwyck, Joel McCrea and Robert Preston. Based on the 1936 novel Trouble Shooter by Western fiction author Ernest Haycox, the film is about the building of the eponymous railroad across the American West. Haycox based his novel upon the experiences of civil engineer Charles H. Sharman, who worked on the railroad from its start in Omaha, Nebraska in 1866 until the golden spike ceremony on May 10, 1869 to commemorate the joining of the Central Pacific and Union Pacific railroads at Promontory Summit, Utah Territory. The film recreates the event using the same 1869 golden spike, on loan from Stanford University.

The Western is a genre of fiction typically set in the American frontier between the California Gold Rush of 1849 and the closing of the frontier in 1890, and commonly associated with folk tales of the Western United States, particularly the Southwestern United States, as well as Northern Mexico and Western Canada.