Warhammer Age of Sigmar is a miniature wargame produced by Games Workshop that simulates battles between armies by using miniature figurines. Games are typically played on a relatively flat surface such as a dining table, bespoke gaming table, or an area of floor. The playing area is often decorated with models and materials representing buildings and terrain. Players take turns taking a range of actions with their models: moving, charging, shooting ranged weapons, fighting, and casting magical spells; the outcomes of which are generally determined by dice rolls. Besides the game itself, a large part of Age of Sigmar is dedicated to the hobby of collecting, assembling and painting the miniature figurines from the game.

Whereas some wargames recreate historical warfare, Age of Sigmar has a fantasy theme heavily inspired by the fiction of J. R. R. Tolkien and Michael Moorcock. Players' armies fight with medieval-era weaponry and cast magical spells, and the warriors are a mixture of humans and fantasy creatures such as elves, dwarves, and orks.

Age of Sigmar is the sequel to the game Warhammer (specifically Warhammer Fantasy Battle). Due to this, the game contains many of the same characters, themes, and models as its predecessor.

The first edition of Age of Sigmar in 2015 replaced Warhammer Fantasy Battle. Another set released for the first edition was Spire of Dawn, which reused the High Elf and Skaven models from the Isle of Blood (Warhammer 8th edition starter set). The initial release of AoS did not include point values for individual units—these were added later—and instead imbalance was to be mitigated by number of models. If one side started the game with one-third more models than the other, the smaller side could choose a "sudden death" win condition for itself. Summoning new units used the same mechanics as spellcasting and required the dedication of reinforcement points for each summonable unit.

The initial release is notable for having included many absurd rules such as:

Pride of the Reiksguard: Helborg’s skill is as legendary as his moustache is magnificent. You can re-roll any failed hit rolls when attacking with the Runefang so long as you have a bigger and more impressive moustache than your opponent.

Escapist Magazine noted that such ridiculous rules could easily be exploited since nothing in the rules said the moustache had to be real and suggested players buy novelty moustaches to satisfy the condition. Other such rules included re-rolls for players pretending to ride and talk to an imaginary horse, screaming a guttural warcry, and keeping a straight face when their opponent tries to make them laugh. Some contemporary reviews were highly critical of such rules saying that while they may have been intended as jokes to encourage roleplaying, they opened up players to ridicule.

The second edition of AoS was released in 2018 following the Malign Portents event. It brought multiple significant changes to the rules, notably an overhaul of the summoning system, the elimination of reinforcement points, and the introduction of endless spells.