Guild Wars is an MMORPG (Massive Multiplayer Online Role Playing Game) developed by ArenaNet, a software company fully owned by Korean gaming company NCSoft.
Guild Wars is different from most other MMORPGs, though, in that the aspect of grinding common to MMORPGs is absent in this game. As a result, Guild Wars is sometimes classified as a CORPG. You just go through quests and missions to find the items, runes and skills you need.
Furthermore, unlike World of Warcraft and other MMORPG's, Guild Wars does not charge a monthly fee for playing the game. Instead, ArenaNet aims to support their online service through the release of two expansion packs (a.k.a. "campaigns") per year.
What makes this game competitive is the Player vs Player and Guild vs Guild battles, and an international tournament called Hero's Ascent. HA is where the five territories (America, Korea, Europe, Japan, and Taiwan/Macao/Hong Kong) fight each other to win Favor of the Gods in the Hall of Heroes. Success in these PvP battles depends very heavily on your choice of skills and the tactics you execute.
By now, there are three different campaigns available:
An expansion to those campaigns, Guild Wars Eye of the North, has been in development since the summer of 2006.