Included under the terms of the agreement, Activision has acquired the publishing rights to Day of Defeat, a multiplayer game powered by Valve's Half-Life technology. Day of Defeat is scheduled for release this May.

"Valve has a proven track record of creating ground-breaking games with worldwide appeal," said Larry Goldberg, executive vice president of Activision Worldwide Studios. "We share with Valve the common goal of delivering the best games possible and with the upcoming launch of Day of Defeat we look forward to kicking-off a strong and successful partnership."

"Activision has been a pioneering games publisher since the days of the Atari 2600, and the company has never been more influential than it is today," said Gabe Newell, co-founder and managing director of Valve. "It's an honor to enter this new partnership and have the opportunity to take Day of Defeat, an ambitious product born of the MOD community, to gamers around the world in a great retail offering."

Day of Defeat is a World War II multiplayer first-person action game that pits players in Axis vs. Allies battles in Western Europe at the height of the war in 1944. Players enlist as snipers, infantrymen, machine gunners, riflemen and sergeants, and then hit the frontlines running using authentic weaponry. The game, which initially debuted as a MOD, features multiple modes of play, a total of 15 multiplayer maps of action -- including 10 new maps, all new character models, hundreds of new animations, increased textures and all new particle effects system. Day of Defeat will also launch with a new Allied squad -- the British.