Codex (plural codices) is the name of a source book for Warhammer 40000 armies and factions containing background information, pictures, and rules.

General Info

Since its creation in the 80's Warhammer 40,000 has had 4 distinct versions or editions. With each edition the Codex of each army has changed to reflect the new rules and units.

First Edition

While the term Codex was not yet used a number of books were comparable. Like the more modern editions they included units and rules which were compiled from the White Dwarf magazine.

Overview
File:Chapter.jpg Book of the Astronomican	File:439px-WH40KCompilation.jpg Compilation	Compendium	Slaves to Darkness	The Lost and the Damned
	Waaargh: Orks	Ere We Go	Freebooterz

Second Edition

The second edition of Warhammer 40,000 was substantially more colorful and the new Codex books reflected this. More detail, such as background information and organization, was included adding more depth to the Warhammer 40,0000 universe.

Overview
Codex: Ultramarines (2nd Edition)	Codex: Angels of Death (2nd Edition)	Codex: Space Wolves (2nd Edition)	Codex: Sisters of Battle (2nd Edition)	Codex: Imperial Guard (2nd Edition)
Codex: Chaos (2nd Edition)	Codex: Eldar (2nd Edition)	Codex: Orks (2nd Edition)	Codex: Tyranids (2nd Edition)

Besides the regular army books there were others that carried the title codex. A codex for the basic style of play, various army lists, and rules were published.

Third Edition

The third edition of Codices were much smaller and less detailed than the second. There is one exception in the designations, the Ork Codex became the Ork Kodex.

Overview
Codex: Space Marines (3rd Edition)	Codex: Orks (3rd Edition)	Codex: Imperial Guard (3rd Edition)	File:Codex chaos marine 3e.gif Codex: Chaos Space Marines (3rd Edition)	Codex: Eldar (3rd Edition)
Codex: Tyranids (3rd Edition)	Codex: Dark Eldar (3rd Edition)	Codex: Dark Angels (3rd Edition)	Codex: Catachans (3rd Edition)	Codex: Blood Angels (3rd Edition)
	Codex: Craftworld Eldar (3rd Edition)	Codex: Space Wolves (3rd Edition)	Codex: Armageddon (3rd Edition)	Codex: Assassins (3rd Edition)

Revision

Within the third edition another group of codices were published. Apart from more pictures and background information, new types of codices were introduced. Rather then providing information on a specific force, these included new rules and background for environments or planetary campaigns.

Overview
Codex: Chaos Space Marines (4th Edition)	Codex: Daemonhunters (3rd Edition)	File:Codex Imperial Guard 4th FCover.jpg Codex: Imperial Guard (4th Edition)	Codex: Witch Hunters (3rd Edition)	Codex: Necrons
	Codex: Cityfight	Codex: Eye of Terror	Codex: Tau (3rd Edition)

Fourth Edition

With the introduction of the 4th edition of Warhammer 40,000 more Codices have been released, so far they include:

Overview
Codex: Space Marines (4th Edition)	Codex: Tyranids (4th Edition)	Codex: Black Templars (4th Edition)	Codex: Tau Empire (4th Edition)	Codex: Eldar (4th Edition)	Codex: Dark Angels (4th Edition)