Quake III Arena (also known as Quake 3; abbreviated as Q3A or Q3), is a multiplayer first-person shooter computer and video game released on December 2, 1999. The game was developed by id Software and featured music composed by Sonic Mayhem and Front Line Assembly. Quake III Arena is the third in the series and differs from previous games by excluding a traditional single-player element and focusing on multi-player action. The single-player is instead played against computer controlled bots in a similar style to Unreal Tournament.

Notable features of Quake 3 include the minimalist design, lacking rarely used items and features, the extensive customizability of player settings such as field of view, texture detail and enemy model, and advanced movement features such as strafe and rocket-jumping.

Quake 3 is available on a number of platforms and contains mature content. The game was highly praised by reviewers who, for the most part, described the gameplay as fun and engaging. Many liked the crisp graphics and focus on multiplayer. The game engine has been heavily modified.

Quake 3 has also been used extensively in professional electronic sports tournaments such as Quakecon, Cyberathlete Professional League and the Electronic Sports World Cup.