The Citizen Kane trailer is a four-minute, self-contained, "making of" promotional short film by Orson Welles and the Mercury Theatre, released in 1940 to promote the film Citizen Kane. Unlike other standard theatrical trailers of the era, it did not feature any footage of the actual film itself, but was a wholly original pseudo-documentary piece. It is considered by numerous film scholars such as Simon Callow, Joseph McBride and Jonathan Rosenbaum to be a standalone short film, rather than a conventional "trailer", and to represent an important stage in developing Welles's directorial style.

The Mercury Theatre was an independent repertory theatre company founded in New York City in 1937 by Orson Welles and producer John Houseman. The company produced theatrical presentations, radio programs and motion pictures. The Mercury also released promptbooks and phonographic recordings of four Shakespeare works for use in schools.