Valve have today announced that Left 4 Dead 2, the sequel to the highly acclaimed Left 4 Dead, is in development.

Coming exclusively to Xbox 360 and PC on November 17, the title adds melee combat to enable deeper co-operative gameplay, with items such as a chainsaw, frying pan, axe, baseball bat, and more.

"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, Left 4 Dead 2 will set a new benchmark for cooperative action games."

With the AI Director 2.0, Left 4 Dead 2's 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.

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.

For more information, check out the official site - we've mirrored the announcement trailer at GP Downloads (118MB).