Survival Mode

Survival Mode is a new mode which was released in the new Downloadable Content from Valve Corporation; the Survival Pack. This gametype throws waves and waves of the Infected at the Survivors until they die. There is no way to really win this through surviving, but instead the goal is to survive as long as you can and set new records.

There are currently sixteen different maps to play on in Survival Mode, fifteen come almost directly from the campaign mode while a new map called The Lighthouse, which was released with the pack, but appears to be attributed with something called The Last Stand. All of the maps have been modified to essentially trap the Survivors into the designated area. Doors have been blocked off, and most choke points such as closets have been removed, leaving the players out in the open. It is possible that, in the future, more maps will be released for the gametype, perhaps filling out the campaigns in entirety.

Game Play
Each survival match starts with a setup time, allowing time for you and your team to scour the map for useful items. The teams will find four health kits, tier 2 weapons, pipe bombs and molotovs, pills, propane tanks, and gasoline tanks scattered around the area. You can take as much time as you want, as the timer at the top of the screen doesn't begin until someone hits the button that alerts the horde. Once the button (typically in the form of a radio) is pressed, the action gets off to a furious start and escalates from there.

As always, teamwork and staying together are necessary for survival. Beyond that, survival strategies vary from map to map and from team to team. It is possible to obtain a Gold Medal achievement by staying in one area of a map, but some may find it more advantageous to move from room to room in order to get more items and ammo. Difficulty increases with time as supplies dwindle, and surviving often involves fending off multiple Special Infected and at times, multiple Tanks.

No Mercy

 * The Generator Room
 * The Gas Station
 * The Hospital
 * The Roof Top

Death Toll

 * The Floodgate
 * The Church
 * The Street
 * The Boat House

Dead Air

 * The Crane
 * The Construction Site
 * The Terminal
 * The Runway

Blood Harvest

 * The Warehouse
 * The Bridge
 * The Farmhouse

The Last Stand

 * The Lighthouse

Achievements
With the introduction of the Survival map, new achievements have been added. There are three milestone achievements: Bronze at 4 minutes, Silver at 7 minutes and Gold at 10 minutes. These were based on the length of time that Valve engineers could survive on their own maps.