Left 4 Dead 2 is a cooperative first-person shooter video game developed and published by Valve Corporation. The sequel to Turtle Rock Studios's Left 4 Dead. Left 4 Dead 2 focuses on four new Survivors, fighting against hordes of zombies, known as the Infected, who develop severe psychosis and act extremely aggressive. The Survivors must fight their way through five campaigns, interspersed with safe houses that act as checkpoints, with the goal of escape at each campaign's finale.