Background
The Codex: Ultramarines was the first rulebook devoted exclusively to Space Marines. While it focused on the Ultramarines Chapter, it was designed to be compatible with any Codex-compliant Space Marine army. The army structure introduced in Codex: Ultramarines would go on to form the basis of the standard format later used in Codex: Space Marines, setting it apart from the unique army formats found in its contemporaries, Codex: Angels of Death and Codex: Space Wolves.