Left 4 Dead is a cooperative first-person shooter video game. It was developed by Turtle Rock Studios, which was purchased by Valve Corporation during development. The game uses Valve's proprietary Source engine, and is available for Windows and the Xbox 360. Development on the game was completed on November 13, 2008 and was released on November 18, 2008 in the United States and on November 21, 2008 in Europe.
Set during the aftermath of an apocalyptic pandemic, the game pits its four protagonists—dubbed "the Survivors"—against hordes of the infected. There are four game modes: a single-player mode in which allied characters are controlled by AI; a four-player, co-op campaign mode; an eight-player on-line versus mode; and a four-player survival mode. In all modes, an artificial intelligence (AI), dubbed the "Director", controls level pacing and item spawns, in an attempt to create a dynamic experience and increase replay value.