Set in a modern day survival-horror universe, the co-operative gameplay of Left 4 Dead™ casts four survivors in an epic struggle against hordes of swarming zombies. The team of four survivors may be comprised of one to four human players, allowing for single player and multiplayer co-op games.

The next-generation A.I. technology of all non-player Survivor and zombie characters is a pool of systems used to procedurally generate a unique experience by monitoring the players' experiences and tailoring the pacing and difficulty of action for each game. This makes for a different experience each time the game is played.