A codex (pluralized as codexes by Games Workshop), in the Warhammer 40,000 tabletop wargame, is a rules supplement containing information concerning a particular army, environment, or worldwide campaign. Codices for particular armies were introduced for the second edition of the game. The third edition rendered these obsolete, and a new series began, including introducing codices for battle zones and campaigns. Until superseded by newer versions, the 3rd edition and later codices remained valid for the newer editions of Warhammer 40,000. Games Workshop no longer produce campaign or battle zone codices, instead releasing 'expansions'. 'Codex' is now a term solely used for army books. At the launch of 8th edition all previous codices were replaced with index books due to a major rules overhaul (as of November 2019 these indexes are no longer produced). The indexes were subsequently replaced by a new series of codices. As before, these codices remain valid until superseded by newer versions (currently the oldest valid codexes are Codex: Astra Militarum - 8th Edition and Codex: Craftworlds - 8th Edition, released simultaneously). The format of the codices has varied somewhat over the years. The most common elements between iterations include: Background - Information about the force and its place in the Warhammer 40,000 universe. This includes artwork, short stories, and copies of fictional documents from the future. Miniature Showcase - Originally a hobby section providing information on collecting, building and painting an army. Later a selection of photographs of Citadel Miniatures painted by Games Workshop's 'Eavy Metal team. Rules - Delivered in varying forms between editions. In earlier editions: a bestiary (descriptions of units, characters and vehicles with special rules and background information), alongside an army list (providing options and points costs for units in the bestiary). Since 7th edition, rules for each unit have been delivered on a datasheet (a concise page detailing all stats, equipment, options and special rules for a unit). All other army rules and points are listed separately in sections before and after the datasheets. Codex supplements provide additional rules for sub-factions of a parent army. These might include special characters or units and other special rules that are only available to that particular sub-faction. Rules for models produced by Forgeworld are available as part of the Imperial Armour series of books, also published by Forgeworld. Rules for models no longer supported by codices and supplements can be found in Warhammer Legends