From Lexicanum

Codex (plural codices or codexes) is the name of a source book for Warhammer 40,000 armies and factions containing background information, pictures, and rules.

Contents 1 General Info 1.1 First Edition 1.2 Second Edition 1.3 Third Edition 1.3.1 Revisions 1.3.2 Campaign and Settings 1.4 Fourth Edition 1.4.1 Campaigns and Expansion 1.5 Fifth Edition 1.5.1 Campaigns and Expansion 1.5.2 Yet to be released Codices include:

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
Book of the Astronomican	Compilation	Compendium	Slaves to Darkness	The Lost and the Damned
	Waaargh: Orks	Ere We Go	Freebooterz

Second Edition

The second edition was substantially more colorful and the new Codex books reflected this fact. More detailed information, such as background and organization, was included, adding more depth and details 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)	Codex: Assassins (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: Blood Angels (3rd Edition)	Codex: Dark Angels (3rd Edition)	Codex: Space Wolves (3rd Edition)	Codex: Chaos Space Marines (3rd Edition, 1st Codex)
Codex: Imperial Guard (3rd Edition, 1st Codex)	Codex: Catachans (3rd Edition)	Codex: Assassins (3rd Edition)	Codex: Orks (3rd Edition)	Codex: Tyranids (3rd Edition)
Codex: Eldar (3rd Edition)	Codex: Craftworld Eldar (3rd Edition)	Codex: Dark Eldar (3rd Edition)	Codex: Witch Hunters (3rd Edition)	Codex: Daemonhunters (3rd Edition)
Codex: Tau (3rd Edition)	Codex: Necrons

Revisions

Some codexes were amended or rewritten during 3rd edition.

Overview
Codex: Dark Angels (3rd Edition Revised)	Codex: Dark Eldar (3rd Edition Revised)	Codex: Imperial Guard (3rd Edition, 2nd Codex)	Codex: Space Marines (3rd Edition, 2nd Codex)

Campaign and Settings

Within the third edition a new type of codices were published. Rather then providing information on a specific force, these included new rules and background for environments or planetary campaigns.

Overview
Codex: Armageddon (3rd Edition)	Codex: Eye of Terror	Codex: Cityfight

Fourth Edition

With the introduction of the 4th edition of Warhammer 40,000 the Codices have been updated and re-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)	Codex: Blood Angels (4th Edition) cover from .pdf	Codex: Chaos Space Marines (4th Edition)	Codex: Orks (4th Edition)	Codex: Chaos Daemons (4th Edition)

Campaigns and Expansion

As in 3rd edition, the 4th edition of the rules also has introduced codexes that deal more than with a single force, but rather expand the rules for select settings and situations.

Overview
Cities of Death	Apocalypse

Fifth Edition

Overview
Codex: Space Marines (5th Edition)

Campaigns and Expansion

Overview
Apocalypse Reload

Yet to be released Codices include:

• Codex: Dark Eldar (5th Edition)
• Codex: Space Wolves (5th Edition)