Left 4 Dead 2 (abbreviated as L4D2) is a cooperative first-person shooter video game and the sequel to Valve Corporation's award-winning Left 4 Dead. Left 4 Dead 2 focuses on four new Survivors, fighting against hordes of the Infected, who develop severe psychosis and exhibit zombie-like tendencies. 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.