Guild Wars is an episodic series of multiplayer online role-playing games, for the Microsoft Windows operating system, created by ArenaNet, a Seattle game development studio and a subsidiary of the South Korean game publisher NCsoft. As of June 2007, three episodes (called campaigns) have been released. Each campaign features a particular continent of a common fictional game world, and premieres new classes, mechanics, and competitive modes. A fourth campaign was known to be in production, but was later replaced with an expansion pack.

Although strictly a massively multiplayer online role-playing game (MMORPG), Guild Wars has important differences from other games in this genre; to emphasize these distinctions, ArenaNet calls the Guild Wars games competitive online role-playing games (CORPGs). Primary among the differences from other commercial MMORPGs is that Guild Wars has no subscription fees: players are offered unlimited playing time on the game servers and their accounts never expire. Guild Wars also has several features designed to promote casual play by reducing grind: low maximum levels, instanced game zones, player-managed NPC henchmen (similar to bots), and instant travel between in-game outposts, for example.

A key design goal for Guild Wars is "balanced competitive gaming". Player characters may be created at the maximum level specifically for player versus player (PvP) matches, and equipment and skills in the game are balanced to ensure a level playing field for such characters. ArenaNet monitors the usage of the gameplay elements and publishes regular game updates to maintain balance and promote variety in competitive strategies and tactics. ArenaNet regularly hosts official Guild Wars tournaments where the most successful player guilds may compete for the chance to play live at gaming conventions and win cash prizes up to 100,000 USD.