The Horus Heresy is a collection of novels, novellas, short stories, audio dramas, game books, and artwork created by some of the Black Library's best-known authors and artists. It chronicles the history of the Horus Heresy era which serves as the foundation and starting-point for most Warhammer 40,000 canon.

The series began in 2006 with the publication of Dan Abnett's Horus Rising and as of 2019 will consist of 54 novels, twenty-four novellas, forty-seven audio dramas, and a large number of short stories written by over nineteen different authors. The Horus Heresy series concluded in February 2019 with the release of the 54th full-length novel, The Buried Dagger by James Swallow.

The series was re-booted and re-branded as The Siege of Terra, which served as the series' finale set during the Battle of Terra.