From the announcement:
Chaos Space Marines are corrupt and treacherous super-warriors hell-bent on tearing apart the Imperium. Though they once strode the galaxy as noble defenders of Mankind, a lifetime of unremitting war has driven them to worship the gods of Chaos. These fell deities have rewarded them with arcane powers, daemonic war marines and hellish weaponry with which to slaughter the armies of the Emperor.
This is a landmark day. On Advance Order is our first ever hardback Warhammer 40,000 Codex as well as astonishing new plastic kits. Codex: Chaos Space Marines is a high quality tome that contains 104 full-colour pages. It comes with the full background and rules for the forces of the Chaos Space Marines, including a gatefold reference page, incredible artwork and a stunning miniatures showcase.