Codex may refer to:
- Codex Ultimatus, a book from the Exam Centre that unlocks threshold abilities
- Rewards bought from the Armoursmith on Mazcab:
- Rewards from the Dragonkin Laboratory:
- Reprisal Ability Codex, an item dropped by Telos, the Warden
- Dormant Zamorakian Ability Codex, a removed item once dropped by Telos, the Warden
- Praesul codex, an item dropped by Nex: Angel of Death
- Slayer Codex, an item used to track Slayer monsters killed
- The Codex, an Elder Artefact