The Mercury Theatre was a theatre company founded in New York City by Orson Welles and John Houseman. They had initial success in the theatre, then went to radio in 1938 as The Mercury Theatre on the Air, a series that included one of the most notable radio broadcasts of all time, The War of the Worlds.

In addition to Welles and Houseman, The Mercury Theatre troupe included Joseph Cotten, Martin Gabel, Alice Frost, Ray Collins, Paul Stewart, Virginia Welles, George Coulouris, Agnes Moorehead and Everett Sloane. Much of the troupe would later appear in Welles' films at RKO, particularly Citizen Kane and The Magnificent Ambersons. Other future stars of the stage, screen, and television, like Betty Garrett and Norman Lloyd, also appeared in productions in smaller parts.