Orcs Must Die! is an action, strategy video game developed and published by Robot Entertainment. It is a tower defense game that eschews the traditional top-down view of similar games, instead using a third-person action-oriented viewpoint.

Orcs Must Die! is a variant of a tower defense game; the player, as the War Mage must defend one or more Rifts on each level from an onslaught of orcs and other creatures that emerge from one or more entrances and traverse the level.

Generally, each orc that reaches a Rift deducts a point from the starting Rift Score while specialized orcs may take off more points; if the Rift Score drops to zero, the level is lost and the player will have to start again.

The orc armies arrive in increasingly more difficult waves, with each level having between four to twelve waves. In general, waves will begin a few seconds after the player defeats the prior one, but roughly every three waves on all bar Nightmare difficulty, the player is given a break where they can set up traps and initiate the next wave when they are ready.