Left 4 Dead (often abbreviated L4D) is a co-op first person shooter developed by Turtle Rock Studios, which was purchased by Valve Corporation during development. The game makes use of the Source Engine, and was released as a downloadable digital version on October 17, 2008

Left 4 Dead (often abbreviated to L4D) is a co-op zombie first person shooter developed by Turtle Rock Studios (purchased by Valve Corporation during development) and based on the Source Engine.

Released in 2008, It was downloadable on PC from October 17, and available Retail for Windows & Xbox 360 on October 18 (North America & Australia) & October 21 (Japan & Europe). It was later released for Mac OS-X on September 27, 2010


The game is based in the aftermath of an apocalyptic pandemic, with the player as one of four protagonists who are immune (but still carry the virus), called "Survivors" in game:

  • Bill, a Vietnam veteran
  • Zoey, a college student
  • Louis, an IT analyst
  • Francis, an outlaw biker

Players are challenged by enemies known as 'infected' -humans who have been infected with a rabies-like virus. There are two main types of infected: common infected, weak on their own but overwhelming in a horde, and 'boss' infected, which are slightly tougher and have special abilities. The boss infected are:

  • Boomer - Survivors can be covered in it's bile - which attracts hordes of common infected to attack. The boomer can vomit on the survivors, or be blown up near them in order to cover them in bile.
  • Hunter - Hunters can pounce on survivors, pinning them to the ground and tearing at them to cause damage. A survivor is helpless whilst pinned; the hunter must be killed or knocked off the survivor with a melee attack to stop the attack
  • Smoker - The smoker can ensnare survivors with its long tongue from a distance, pulling them toward itself. if the survivor gets stuck along the way (such as behind a car), the tongue will start constricting and damaging the survivor, otherwise it will continue to drag them until it can hit them with it's arms. The Survivor is helpless when caught, and either the smoker must be killed, the tongue shot or the trapped survivor melee'd in order to free them.
  • Witch - The witch lies in wait, and ignores the survivors if they keep a distance, and don't shine light on her. When startled, she will chase down the original survivor who startled her, and (depending on the difficulty setting of the current game) either incapacitate or kill that survivor. If incapacitating, the witch will continue to tear at the survivor until either it or the survivor has been killed.
  • Tank - A massive hulk-like infected, the tank can throw chunks of ground at the survivors, or punch them to send them flying. It can also hit some (otherwise) immovable objects, such as cars and dumpsters, which will instantly incapacitate survivors if they are hit by them.

When playing versus, opposing players take control of boss infected (excluding the Witch)

Game Modes Currently there are four game modes:

  • Single player- One player along with 3 AI-controlled bots
  • Co-Op Campaign- The same as single player, however up to four human players can take part
  • Versus Mode- Players play as both Survivors and Infected, with up to 8 players
  • Survival Mode- 4 players being attacked by Infected in waves


Left 4 Dead is a first-person shooter. The game is focused on cooperation and team play, as such any survivors not currently being played are filled in by AI-controlled bot characters. Colored outlines of teammates are visible through walls to help players stick together and coordinate their movement. If a survivor falls off a ledge, then they may automatically hang onto it and can only be helped up by another survivor.

  • In campaign/single player modes, the player takes control of one of the survivors. They play through the levels fighting off the infected.
  • In versus mode, two teams take turns playing as the survivors and as the infected, swapping sides once per chapter. Unlike campaign mode, dead survivors cannot re-spawn mid-chapter

The game dynamics, difficulty and pacing are tweaked and controlled based upon in-game factors by a dynamic system known as the 'AI Director'.

Instead of fixed places, the Director places enemies and items in varying positions and quantities based upon each player's current situation, status, skill and location. The Director also creates mood and tension with emotional cues, such as visual effects, dynamic music, and character communication. This helps to create a different experience for each playthrough.

In addition to the AI Director, there is a second Director that controls music. It was created as a way to keep the music interesting throughout the game. The music Director monitors what a player has experienced to create an appropriate mix. The process is client-side and done by a multi-track system. Each player hears their own mix, which is being generated as they play through the game, and dead players watching a teammate hear their teammates' mix.