Warmaster is a ruleset for tabletop wargames written by Rick Priestley, published by Specialist Games (a division of Games Workshop), and set in the Warhammer Fantasy setting. It is different from Warhammer Fantasy Battles in both appearance and gameplay. It is intended for 10 –12 mm miniatures. Basic troops are based on stands, of which typically three make a unit. Generals, Heroes and Wizards are mounted individually or with their retinue.

Gameplay focuses on command and control. While magic is used in the game, its effect on the game is limited. The game is designed to focus on the general's ability to command rather than just his army's ability to fight.

In the Warhammer 40,000 universe, Epic fills much the same "large scale battle" role as Warmaster does in Warhammer Fantasy, though the two systems do not share rules, and Epic is intended for slightly smaller 6 mm miniatures.

The original version, the fantasy ruleset Warmaster, was first released in 2000. As with most of the "specialist" games products, the support strategy from Games Workshop has evolved over time. Once a part of the Specialist Games division, Warmaster was then directly supported by Games Workshop itself, albeit at a reduced level. In 2013 Games Workshop stopped producing the miniatures and started to remove them from their webstore as stocks ran out. A freely downloadable "Living Rulebook", along with supplements and archived magazine articles, are available through the fan-administered site Specialist Games.

In mid-2006, a new online supplement was added to the Specialist Games website, known as Warmaster Armies. This supplement includes slightly revised lists for the six original armies (High Elves, Empire, Dwarfs, Chaos, Orcs and Goblins, and Tomb Kings of Khemri), alongside new lists for eight forces (Dark Elves, Skaven, Bretonnians, Lizardmen, Kislevites, Vampire Counts, Daemonic Hordes, and Araby).

This was followed in 2009 by a fan-based supplement release. This included a large number of alternative, trial or fan designed army lists. The Warmuster publication aimed to promote ongoing development of the game but has since been superseded and refined (see below for Warmaster Revolution).

In 2010 Warmaster 2nd Edition was released, which compiled and clarified the siege rules written for the game over the preceding 10 years.

Since 2017 a revamped ruleset was released by the Warmaster community called Warmaster Revolution. Bringing together elements of Warmaster Ancients and some extra 'house rules', Warmaster Revolution has quickly established itself as the ruleset of choice for Warmaster players. Its release coincided with a marked upturn of interest with the game, due in no small part to the launch of Warmaster Podcast in 2016. With a growing FB community, YouTube videos and more tournaments globally, Warmaster is experiencing a renaissance with an expanding base of new converts and returning players. The new ruleset incorporates many of the 2009 supplement army lists but has a working committee that looks to refine the lists to make them balanced and playable as well as tweak current army lists.