The planet on which Edward and Altaira Morbius live is Altair IV, which according to Star Trek: Deep Space Nine is also a Federation planet. Director Fred M. Wilcox consulted with scientists before making the decision that the planet's sky would be green.
The reaction from the preview audience to this film was so positive that it was released as it was, with no further changes to the movie. The result is that there are several rapid takes toward the story's end.
The scene in which the image of Altaira appears in the Krell's "plastic educator" device was achieved with several special effects, including superimposed film footage of the charge from an electrical generator, hand-drawn animation, and a traveling matte cut from film footage of Anne Francis.
The Spaceship C57D, models and full-size prop was actually used in seven episodes of The Twilight Zone. The list is as follows by season, "Third from the Sun", "The Monsters Are Due on Maple Street", "The Invaders", "To Serve Man", "Hocus-Pocus and Frisby", "Death Ship" and "On Thursday We Leave for Home". Robby's vehicle does appear in one episode. In "The Rip Van Winkle Caper", at the end when the final surviving gold thief is dying, a futuristic car stops and he begs for water. This is Robby's vehicle. The crew's outfits were used in a number of episodes, not to mention also in The Time Machine along with some props. The flickering force-field fence-posts appeared in Atlantis, the Lost Continent and were last seen being placed at the bottom of the ocean in Around the World Under the Sea.
The special effects artists used split-screen traveling mattes to make images appear and disappear, such as the piece of fruit Morbius lobs at the "household disintegrator beam" and the tiger that Commander Adams vaporizes. See the "Goofs" section for problems caused by this process.
The time aboard the C57D is stated as being 17:01 hours when the ship enters orbit around Altair IV. Gene Roddenberry, a fan of this movie, would later use 1701 as the naval construction contract number of the Starship Enterprise.
The trailer for this film was narrated by Marvin Miller, who also provided the voice for 'Robby The Robot'.
This film marked one of the first times a science fiction project had received a large budget. The genre had rarely been taken seriously by studio executives, and had generally received the most meager of budgets. The critical success of this film convinced many in the film industry that well-funded science fiction projects could be successful. Film historian Ben Mankiewicz has claimed that Forbidden Planet's success made future big-budget science fiction films possible.
This movie was filmed on the same sound-stage on which the movie The Wizard of Oz had been filmed seventeen years earlier; the set of Altaira's garden is a reuse of the Munchkin Village set from The Wizard of Oz.
To increase the sense of depth, the opening image of the spaceship approaching the camera is actually composed of two shots: the first of a small model, the second of a larger model travelling on the same track. The ship passes into and out of a shadow to conceal the cut.
Writers and special effects artists Irving Block and Allen Adler originally conceived of this film as a B picture and brought it to Allied Artists, which turned it down. They then decided to try their luck at MGM, then still Hollywood's most prestigious studio, which had not produced a science fiction film since The Mysterious Island (1929). To their surprise, studio chief Dore Schary green-lighted the project, immediately catapulting the film to the status of a major production.