Most of the images used in the assassin training montage were of anonymous figures or patriotic backgrounds, with occasional historical individuals such as Richard Nixon, Adolf Hitler, Pope John XXIII, and Lee Harvey Oswald (in the picture taken moments after his shooting). The montage also uses a drawing by Jack Kirby of the Marvel Comics character Thor. The drawing is a cropped image from the cover of Thor Annual #4 (December 1971), which in turn is a reprint of the cover image from Thor #131, "They Strike from Space" (August 1966). The montage also includes a cropped image from the cover of Thor #135 (December 1966) featuring a creature known as the Man-Beast.
The film was nearly unable to begin production at all because the screenplay was not ready when Warren Beatty had marked in the start of filming, and with a Writers Guild of America strike looming Paramount was leaning towards shuttering the project altogether. However, Beatty did single-handed rewrites with the help of Robert Towne (this would later become controversial because Towne's many enemies in Hollywood began spreading rumors that he had crossed the WGA picket line and continued to work with his longtime friend and collaborator on the film) and the movie did get underway and was able to finish on time.
The distinctive anamorphic photography, with long lens, unconventional framing, and shallow focus, was supervised by Gordon Willis.
The river scene was filmed at the Gorge Dam, on the Skagit River (Ross Lake National Recreation Area) in Washington State. (48 41' 51" N, 121 12' 29" W)
The Space Needle in Seattle is seen extensively in the first assassination sequence.
The airport scene was filmed at Bob Hope Airport in Burbank, California.