The Strange World of Planet X (U.S. title: Cosmic Monsters) is an independently made 1958 British second feature ('B') science fiction horror film directed by Gilbert Gunn and starring Forrest Tucker and Gaby André. It was adapted by Paul Ryder and Joe Ambor from the 1957 Rene Ray novel of the same name, produced by George Maynard and John Bash and distributed in the UK in February, 1958 by Eros Films. It was released in the US on July 7, 1958 by Distributors Corporation of America as a double feature with The Crawling Eye, also starring Tucker.

A made-for-TV serial, adapted by Rene Ray in 1956, had aired previously in the UK and was the basis for the feature film.

A monomaniacal scientist creates ultra-sensitive, disruptive magnetic fields, which have unexpected side effects, while also attracting unidentified flying objects from outer space. Strange things begin to happen, including a freak storm, blasts of cosmic radiation that penetrates the Earth's normally protective magnetic shield, and insects and spiders mutating into giant flesh-eating monsters.