Orson Welles called this his best film.
Orson Welles originally wanted Jackie Gleason to play the advocate. Welles was going to play the priest, which would have made the fable in the beginning be further justified.
Orson Welles reportedly dubbed a few lines of 'Anthony Perkins'' dialog. Perkins later said he could never figure out which lines they were.
Audio sample of K being interrogated by the police at the beginning of the film was used by the band Burning Airlines on a track called "My Pornograph".
In the novel, K is killed with the knife, but Orson Welles felt that was inappropriate with the Holocaust in recent memory, so he changed it for the film.
It has been reported that Orson Welles dubbed 11 voices in the movie.
The "pin-screen," also called the "pin-board," used in the opening and closing sequences was invented by Alexander Alexeieff in the early 1930's. It is a board with pins stuck in it at regular intervals. The pins can be raised or lowered to form an image, which can then be lit and photographed. By manipulating the pins and photographing them one frame at a time, the device can be used for animation, and though it was not so used in "The Trial" Alexeieff and Claire Parker made at least two short animated films using the pin-screen, _nuit sur le mont chauve, Une (1933)_ and Le nez.
The scene of K's office was filmed in the Paris train station, Gare d'Orsay, shortly after it was closed and before it became an art museum.
Welles told Peter Bogdanovich in "This Is Orson Welles" that "there's not a single symbol" in "The Trial".