It Conquered the World is an independently made 1956 American science fiction film produced and directed by Roger Corman, and starring Peter Graves, Lee Van Cleef, Beverly Garland, and Sally Fraser. Shot in black-and-white, It Conquered the World was released theatrically by American International Pictures (AIP) as a double feature with The She-Creature.

It Conquered the World concerns an alien creature from the planet Venus that secretly wants to take control of the Earth. The creature makes radio contact with a disillusioned human scientist, who agrees to help because the scientist believes that such an alien intervention will bring peace and save a doomed humanity from itself.

Dr. Tom Anderson, an embittered scientist, has made contact with a Venusian creature, while using his radio transmitter. The alien's secret plan is to take complete control of the Earth by enslaving humanity using mind control devices; the alien claims that it merely desires to bring peace to the world by eliminating all emotions. Anderson agrees to help the creature and even intends to allow it to assimilate his wife Claire and friend Dr. Paul Nelson. The Venusian disrupts all electric power on Earth, including motor vehicles, leaving Dr. Nelson to resort to riding a bicycle.

After avoiding a flying bat-like creature which carries the mind control device, Dr. Nelson returns home to find his wife, Joan, newly assimilated. She attempts to force his own assimilation using another bat-creature in her possession, and he is forced to kill her in self-defense. By then, the only people who are still free from the Venusian's influence are Nelson, Anderson, Anderson's wife Claire and a group of army soldiers stationed in the nearby woods.

Nelson finally persuades the paranoid Anderson that he has made a horrible mistake in blindly trusting the Venusian's motives, allying himself with a creature bent on world domination. When they discover that Tom's wife Claire has taken a rifle to the alien's cave in order to kill it, they hurriedly follow her, but the creature kills her before they can rescue her. Seeing the loss of everything he holds dear, Dr. Anderson viciously attacks the Venusian by holding a blowtorch to the creature's face; Anderson dies at the alien's hand as it expires. Arriving on the scene too late to save his friend, Nelson sadly reflects on how Anderson's misguided ideals led to death and devastation, and muses that a solution to humanity's problems must ultimately be achieved by humanity itself.

The film was inspired by the box office success of Day the World Ended, also directed by Corman. It was written by Lou Rusoff (Sam Arkoff's brother-in-law), but before being completed, Rusoff's brother died and he had to leave for Canada. Corman then called in Charles Griffith to do a final rewrite, two days before filming began. Griffith does have a small part as a scientist.

Griffith said Rusoff's script "was incomprehensible which was strange because he was quite meticulous. Lou's brother was dying at the time which most likely had something to do with it." Griffith said he "wrote streams of dialogue. The picture was terrible."

Peter Graves' casting was announced in March 1956. Beverly Garland's casting was announced shortly afterwards.