The Three-Body Problem (Chinese: 三体; lit. 'three body') is a 2008 novel by the Chinese science fiction author Liu Cixin. It is the first novel in the Remembrance of Earth's Past trilogy. The series portrays a fictional past, present, and future wherein Earth encounters an alien civilization from a nearby system of three Sun-like stars orbiting one another, a representative example of the three-body problem in orbital mechanics.

The story was originally serialized in Science Fiction World in 2006 before it was published as a standalone book in 2008. In 2006, it received the Galaxy Award for Chinese science fiction. In 2012, it was described as one of China's most successful full-length novels of the past two decades. The English translation by Ken Liu was published by Tor Books in 2014. That translation was the first novel by an Asian writer to win a Hugo Award for Best Novel; it was also nominated for the Nebula Award for Best Novel.

The book has been adapted into other media. In 2015, a Chinese film adaptation of the same name was in production, but it was never released. A Chinese TV series, Three-Body, released in early 2023 to critical success locally. An English-language Netflix series adaptation, 3 Body Problem, was released in March 2024.