A codex is the rulebook and lore bible for one Warhammer 40k faction. It tells you what your models can do, what they cost, and who they are in the setting. If you’re starting an army, it’s the first book you’ll want.
What a codex actually contains
Every codex does three jobs at once. It gives you the background of your faction, shows off painted miniatures, and provides the rules you need to play.
The lore section covers history, characters, and famous battles. You’ll find artwork, short stories, and in-universe documents that build the atmosphere.
The miniatures showcase is a gallery of Citadel figures painted by Games Workshop’s ‘Eavy Metal team. It’s there to inspire your own paint scheme.
The rules section is the practical part. It lists unit profiles, wargear, points values, and special abilities.
- Background: faction history, characters, and lore
- Miniature showcase: painted models for inspiration
- Rules: unit stats, wargear, points, and abilities
How to use it in a game
Start with the army roster. Pick the units you want, then look up their datasheets. Each datasheet gives you movement, toughness, wounds, saves, and weapons.
Points values tell you how much each unit costs. You’ll add them up to build a legal army list for your game size.
Special rules are scattered across the book. Some apply to your whole army, others only to specific units or characters. Read them before you play, not during.
If you’re new, don’t try to memorize everything. Bookmark the datasheets you use most and check the core rules for the rest.
Editions and why they matter
Codices are tied to a specific edition of Warhammer 40k. When a new edition launches, older codices usually stop being valid.
The first army books appeared in second edition. Third edition started a new series and added campaign codices, though those are gone now. Games Workshop only makes army codices these days.
Eighth edition replaced all previous codices with index books during a big rules overhaul. Those indices were later replaced by a fresh run of codices.
Supplements exist too. They add rules for a sub-faction, like a specific Space Marine chapter, without repeating the whole parent codex.
| Edition | What happened |
|---|---|
| 2nd | First army codices introduced |
| 3rd | New series, plus campaign codices |
| 8th | Index books replaced all codices, then new codices followed |
| 10th | Current edition with codices and supplements |
Codices vs. supplements and expansions
A codex covers a whole faction. A supplement narrows in on a sub-faction, like Black Templars or Blood Angels, and usually needs the main codex to work.
Expansions add new ways to play, such as boarding actions or crusade campaigns. They aren’t army books, but they can change how your force plays.
If you’re unsure what to buy, start with the codex for your faction. Supplements and expansions come later, once you know the core rules.
Key facts
- A codex is a rules supplement for one Warhammer 40k faction, containing lore, miniature showcases, and game rules.
- Codices are edition-specific; when a new edition arrives, old ones are usually retired.
- The first army codices appeared in second edition, and third edition introduced campaign codices (now discontinued).
- Eighth edition replaced all codices with index books before starting a new codex series.
- Supplements add rules for sub-factions and usually need the main codex.
- Expansions like Crusade or Boarding Actions add new ways to play but aren’t army books.
FAQ
Do I need a codex to play Warhammer 40k?
Yes, for most factions. The codex has the datasheets and points you need to build a legal army. Some starter sets include basic rules, but a full codex gives you the complete picture.
Can I use an old codex with a new edition?
Usually not. Each edition updates the rules, and older codices are replaced. Check the current edition’s release list before you buy.
What’s the difference between a codex and a supplement?
A codex covers a whole faction. A supplement adds extra rules for a sub-faction and often requires the main codex to use.