The is a foundational background book for the 2nd Edition of Warhammer 40,000, first released in 1993 as part of the core boxed set. Often referred to by veterans as the "Black Book," it served as the primary source for the game's lore (or "fluff") and provided the initial army lists for all major factions before they received their own standalone codexes.
The was not just a rulebook but a comprehensive guide to the Imperium of Man and its numerous enemies. Codex Imperialis 2nd Edition Pdf