Inquisitor is a tabletop miniatures game based in Games Workshop's Warhammer 40,000 Universe. Wheras Warhammer 40,000 is based on squad based tactical warfare Inqusitor focuses on a small group of adventurers and plays like a Role-playing game. Players choose a warband, usually made up of an Inquisitor and his/her henchmen.

The game is supported by Games Workshop's specialist games division, which periodically releases new rules for the game through the specialist games website. The game is intended for older wargamers, aged 16 and up.

Inquistor corebook has very rich and detailed information about Inquisition in WH40K world and Ecclesiarchy in general. The name, when written, is sometimes shortened to =I= by fans, in homage to the symbol of the Inquisition as depicted on the cover of the rulebook.

Inquisitor uses a rules system based around the throwing of hundred-sided dice (sometimes known as D100)

There are, technically, no limitations on the effective power and equipment of a player character - there are no hard and fast rules that prevent a player from creating a character armed with unfeasibly potent combinations of equipment and skills, although the game rulebook includes an optional "points" system that the organisers of a campaign might use to limit their players. Generally, however, it is requested of players that they exercise a modicum of common sense when creating their characters.

Player characters are represented in-game by (comparatively) large-scale miniatures purchased from Games Workshop. the models purchased represent existing characters (such as Witch-hunter Tyrus, or Damien 1427) presented in the rulebook. Players wishing to depict their own unique characters are generally required to extensively convert their models, or give them unique paint schemes.