The People That Time Forgot is a fantasy novel by American writer Edgar Rice Burroughs. The novel is the second of his Caspak trilogy. The novel is a direct sequel to The Land That Time Forgot and continues the lost world saga begun in the earlier story.

Burroughs continues the revelation of his lost world's unique biological system, only hinted at in the previous installment, in which the slow progress of evolution in the world outside is recapitulated as a matter of individual metamorphosis. This system forms a thematic element serving to unite the three Caspak stories.

The novel was adapted to film in 1977 under the direction of Kevin Connor by Britain's Amicus Productions. The movie was the third and last of Amicus' Burroughs adaptations, the others being The Land That Time Forgot (1975), based on the first segment of the Caspak sequence, and At the Earth's Core (1976).

The Caspak trilogy was first published in Blue Book Magazine as a three-part serial in the issues for September, October and November 1918, with this short novel being the second installment. The complete trilogy was later combined for publication in book form in 1924 under the title The Land That Time Forgot. E-book: ePUB, 38 400 words, reading time approximately 3 hours, 10 min. AUDIO: Reading by Ralph Snelson, running time: 3 hours, 47 min. Unabridged full version.

Edgar Rice Burroughs (1875-1950) was an American author, best known for his creation of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.