Principal Lead Systems Designer Damion Schubert has unveiled the Codex in Star Wars: The Old Republic, and it's basically a story-based achievement system. Here are some of the highlights:

• The team had two design goals: providing more fictional context for the player, and providing an explorer mini-game with meaningful rewards.
• It was inspired by the codex systems in Dragon Age and Mass Effect.
• Current estimates of the codex are around 120,000 words of text. The average Star Wars novel comes in at around 100,000 words.
• Some Codex entries will be given away for free. Others will require exploration or killing various monsters.
• Datacrons are unique objects you can find throughout the world that will increase one of your stats permanently.
• The system is designed to be easily expandable.

Check out Schubert's entire blog entry for more details on the Codex.