Horus Heresy is an out-of-print collectible card game originally produced in 2003 by Sabertooth Games. The game is set in the Warhammer 40,000 fictional universe developed by parent company Games Workshop. It attempts to recreate the struggle between the Loyalist forces of the Emperor of Mankind and the Traitor forces of Warmaster Horus, during the civil war known as the Horus Heresy. The game's development and sale by the publisher were discontinued in 2008, following financial difficulties at the parent company.