A Warhammer 40k Codex book is the essential supplement for your army. It packs in the faction’s background, artwork, and all the rules you need to field them on the tabletop. If you’re collecting or playing a specific force, the Codex is your go-to reference.
What’s inside a Codex
Every Codex follows a similar pattern. You get a close look at the faction’s lore, including artwork, short stories, and in-universe documents. There’s also a showcase of painted miniatures from Games Workshop’s ‘Eavy Metal team. The rules section covers unit profiles, wargear, and special abilities, though the exact format has shifted between editions.
- Background: the army’s history and place in the 41st millennium.
- Miniature showcase: photos of Citadel Miniatures painted by the studio team.
- Rules: datasheets for units, characters, and vehicles, plus army-wide abilities.
How codices have evolved
Army-specific codices started with the second edition. The third edition reset the line and introduced books for battle zones and campaigns too. Those campaign codices were later replaced by expansions, and now Codex only refers to army books.
At the launch of eighth edition, a major rules overhaul meant all previous codices were replaced by index books. Those indices were temporary and are no longer produced. New codices followed, and they stayed valid until a newer version came out. The pattern repeats with each edition.
| Edition | Key change |
|---|---|
| 2nd | First army codices introduced. |
| 3rd | Reset; campaign and battle zone codices added. |
| 8th | Indices replaced all codices; new series followed. |
| 10th | Current codices for all major factions. |
Why they matter for players
Without a Codex, you can’t legally field your army in most games. It’s where you’ll find the points values, unit rules, and faction abilities that make your force work. They’re also the main source of lore for your chosen faction, so they’re as much for reading as for playing.
If you’re just starting out, the Codex for your army is usually the first purchase after the core rules. It gives you everything you need to build and play a matched play army.
Codices and the wider lore
Each Codex expands the Warhammer 40,000 universe by focusing on one faction. You’ll learn about their motivations, key characters, and how they fit into the larger setting. That makes them a great entry point if you want to explore beyond the core rulebook.
Because they’re updated with each edition, codices also reflect the current state of the galaxy. Major events like the Great Rift or the return of a primarch often show up in the relevant codex first.
Key facts
- A Codex is a rules supplement for a specific Warhammer 40k army, containing lore, artwork, and game rules.
- Army codices were first introduced in the second edition of the game.
- Games Workshop pluralises them as ‘codexes’, though ‘codices’ is also common.
- At the launch of eighth edition, indices temporarily replaced all codices.
- Codices are updated with each new edition and remain valid until superseded.
FAQ
Do I need a Codex to play Warhammer 40k?
Yes, for most games you need the Codex for your faction. It contains the rules and points values for your units. Without it, you can’t legally field your army in matched play.
How often are codices updated?
Games Workshop releases new codices with each new edition of the game. They stay valid until a newer version replaces them. The current edition is tenth, with codices for all major factions.
What’s the difference between a Codex and an index?
Indices were temporary books released at the start of eighth edition to cover all factions after a major rules overhaul. They were later replaced by full codices. Indices are no longer produced.