Valve has announced that Left 4 Dead 2 is currenlty under development. Left 4 Dead 2 (L4D2) is currently slated for release on the Xbox 360 and PC and promises to be come one of 2009's marquee titles.

 "A large part of how Left 4 Dead became 2008's top-selling new IP on Xbox 360 and the PC was the custom-tailored gameplay made possible by the AI Director," said Gabe Newell, president and co-founder of Valve. "With the knowledge gained from creating the original, new technology, and a passionate team, L4D2 will set a new benchmark for cooperative action games."

Left 4 Dead 2 is set for release on November 17, 2009 and adds melee combat with items such as a chainsaw, frying pan, axe, baseball bat and more. More info after the jump.

From the press release:

Introducing the AI Director 2.0, L4D's dynamic gameplay is taken to the next level by giving the Director the ability to procedurally change weather effects, world objects, and pathways in addition to tailoring the enemy population, effects, and sounds to match the players' performance. The result is a unique game session custom fitted to provide a satisfying and uniquely challenging experience each time the game is played.

Featuring new Survivors, boss zombies, weapons, and items, Left 4 Dead 2 offers a much larger game than the original with more co-operative campaigns, more Versus campaigns, and maps for Survival mode available at launch.

Supported by a $10+ million marketing campaign, Left 4 Dead has sold over 2.5 million retail copies since it was released in November of 2008. Left 4 Dead 2 is targeted for release on Xbox 360 and the PC on November 17, 2009, and will be launched worldwide with a multi-million dollar marketing campaign across TV, Outdoor, and Online.

"Left 4 Dead was backed by our most aggressive advertising campaign to date, and resulted in a top 5 showing on two platforms during holiday 2008," said Doug Lombardi, VP of marketing at Valve. "Left 4 Dead 2 is a larger game and will be supported with even more consumer and retail advertising programs than the original."

Left 4 Dead 2 will be featured as the cover story on PC Gamer and Official Xbox Magazines this month. For more information, please visit www.l4d.com.