The Three-Body Problem (Chinese: 三体; lit. 'Three-Body'; pinyin: sān tǐ) is a science fiction novel written by the Chinese writer Liu Cixin. The title refers to the three-body problem in orbital mechanics. It is the first novel of the Remembrance of Earth's Past (Chinese: 地球往事) trilogy, but the whole series is normally referred to as The Three-Body Problem. The trilogy's second and third novels are The Dark Forest and Death's End respectively.

The first volume of The Three-Body Problem was first serialized in Science Fiction World between May and December 2006. It was published as a standalone book in 2008, becoming one of the most successful Chinese science fiction novels of the last two decades. The novel received the Chinese Science Fiction Yinhe ("Galaxy") Award in 2006 along with many more over the years. By 2015, a Chinese film adaptation of the same name was in production.

The English translation by Ken Liu was published by Tor Books in 2014. Thereafter, it became the first Asian novel ever to win a Hugo Award for Best Novel, and was nominated for the Nebula Award for Best Novel.

The series portrays a future where, in the first book, Earth is awaiting an invasion from the closest star system, which, in this universe, consists of three solar-type stars orbiting each other in an unstable three-body system. Within the system, its single Earth-like planet is being unhappily passed among them and suffers from extremes of heat and cold, as well as the repeated destruction of its intelligent civilizations.