The Forgotten Planet is a science fiction novel by American writer Murray Leinster.

The novel is a fix-up from three short stories, "The Mad Planet" and "The Red Dust", both of which had originally appeared in the magazine Argosy in 1920 and 1921, and "Nightmare Planet", which had been published in Science Fiction Plus in 1953.

A planet had been seeded for life by humans, first with microbes and later with plants and insects.

Groff Conklin of Galaxy Science Fiction praised the novel as "Leinster at his exciting, skilled best," declaring "there is almost nothing in the story that is not first-rate.

"[3] Anthony Boucher, however, found it to be "an interminable sequence of wars against giant insects, which seems pretty outmoded today.