Writer Hans Janowitz claims to have gotten the idea for the film when he was at a carnival one day. He saw a strange man lurking in the shadows. The next day, he heard that a girl was brutally murdered there. He went to the funeral, and saw the same strange man lurking around. He had no proof that the strange man was the murderer, but he fleshed the whole idea out into his film.
Weeks before the initial release of the film, posters with the tag-line "Du mußt Caligari werden!" ("You have to become Caligari!") were put up in Berlin without the slightest hint that they were promotion for the upcoming movie.
In the May 12, 1921 edition of the Chicago Daily News, Carl Sandburg wrote of the film: "It is a healthy thing for Hollywood, Culver City, Universal City, and all other places where movie film is being produced, that this photoplay has come along at this time. It is sure to have healthy hunches and show new possibilities in style and method to our American Producers."
The final look and feel of the film was based as much on low budget practicalities as it was on creative inspiration and expressionism. Electricity was strictly rationed in post WWI Germany at the time the film was being shot. So, Director Robert Wiene ended us simply painting light beams on backdrops. Shooting on severely confined sets, forced him to use unusual camera angles.
The trivia item below may give away important plot points.
Director Robert Wiene added the opening and closing scenes to Hans Janowitz and Carl Mayer original script in order to make the film more commercially viable. (It is often speculated that the "all a delusion" twist was to deflect suspicion that the film painted authority as insane.) Fritz Lang claims to have suggested the introductory scene when first presented with the script.