The Lost Worlds of 2001 by Arthur C. Clarke was published in 1972 by Signet as an accompaniment to the novel 2001: A Space Odyssey.

The book itself consists in part of behind-the-scenes notes from Clarke concerning scriptwriting (and rewriting), as well as production issues. The core of the book, however, is contained in excerpts from the proto-novel and an early screenplay that did not make it into the final version.

Alternative settings for launch preparation, the EVA scene where astronaut Frank Poole is lost, and varying dialogues concerning the HAL 9000 unit are all featured in the book. Also included is the original short story The Sentinel on which 2001 is loosely based.