Warhammer 40,000 (informally known as Warhammer 40K or just 40K) is a tabletop miniature wargame in a science fantasy setting produced by Games Workshop. Warhammer 40,000 was created by Rick Priestley in 1987 as the futuristic companion to Warhammer Fantasy Battle, sharing many of the same game mechanics with periodic expansion sets. The game is currently in its fifth edition.

Players assemble and paint individual scale (approximately 1:72) miniature figures that represent futuristic soldiers, creatures and vehicles of war. These figurines are collected to comprise squads or armies that can be pitted against those of other players. Each player brings a roughly equal complement of units to a 4' by 6' battlefield with handmade or purchased terrain. The players then decide upon a scenario, ranging from simply facing the two armies off against each other to complex battles involving defense and reinforcements. The models are physically moved across the table and actual distance between models plays a role in the outcome of combat. Play is turn based, with various outcomes determined by the roll of dice. Battles may last anywhere from a half hour to several hours, and some players string battles together to form campaigns. Game and hobby stores host games periodically and official tournaments are held on a regular basis.

Warhammer 40,000's gothic space fantasy setting spans a vast fictional universe. Its various factions and races include the Imperium of Man (the human race 40,000 years hence), the Orks (similar to Warhammer Fantasy Orcs), and the Eldar (similar to Elves in Warhammer Fantasy Battle). These races, along with their playing rules, are covered in the game's rule books and supplemental army codexes, along with articles in the Games Workshop magazines, White Dwarf and Imperial Armour. Lines of these miniatures are produced by Citadel Miniatures and Forge World.

The Warhammer 40,000 setting is used for several related games, video games and other works of fiction, including licensed works published by Black Library, a subsidiary of Games Workshop.