63 books in series

The Horus Heresy

The Horus Heresy is a 65-book series with 63 released primary works first released in 9 with contributions by Graham McNeill, Dan Abnett, Ben Counter, James Swallow, Mitchel Scanlon, Mike Lee, Aaron Dembski-Bowden, Gav Thorpe, Nick Kyme, Chris Wraight and 11 others.