Originally Posted by Zombie Panic Source Webesite

The basic idea of the Zombie Panic is to create solid game play that is based on a classic zombie outbreak scenario, the living dead are coming for the last remaining humans, and these survivors must fight them off and live through the day.
The game works like this:
Everyone joins a server, in the beginning you can either choose to join the human team or you can volunteer to be the first zombie. If no one volunteers the game will pick one human randomly and the game begins. The starter zombie's goal is to, of course kill the humans while the human goal is to stay alive as long as possible, complete objectives, or even wipe out all the zombies. The catch is that when a human is slayed he will simply join the ranks of the undead, now ready to finish off his old living teammates.
The humans can't tell by the player list who's alive and who's not, eventually there will only be one survivor still standing if all goes wrong, facing all the zombies which use to be allies, with his back to a wall. The zombies only have a certain number of reinforcements (lives), when a zombie is killed they lose 1 life from the counter. However, when a human is killed they gain 1 life. If the zombies only have 1 respawn left the humans can win the round by killing off the remaining undead left on the map.
This is the main concept of how the game works but of course, but with additional game modes there is a bit more variety to it.