The Codex Astartes is the written doctrine of the Adeptus Astartes – the Space Marines. It defines the proper organization of a Chapter and tactical solutions for any battlefield situation of any scale. The Codex was originally written after the Horus Heresy and subsequent reorganization of the Space Marine Legions by Roboute Guilliman, the Primarch of the Ultramarines, and has been appended by thousands of warriors since. Most known Chapters seem to adhere to the Codex to a high degree. It is considered a holy document among the Astartes.
- Cook, Chris et al. Index Astartes. Nottingham: Games Workshop, 2002.