ZPA mode places two even teams of survivor and zombies against each other to compete for control of areas and objectives. These objectives vary from map to map, as they may be goals such as the survivors defending a location, or the zombies preventing the humans from achieving something, similar to Objective Mode.
What makes this game mode unique is how there is no infecting (the percent chance for infecting a survivor has been replaced with a percent chance to bleed the player to death), zombification, or life count. This means the humans who are killed will still respawn as humans, and zombies who are killed will still respawn as zombies without any consequences.
The round is won if one team successfully thwarts the other teams' goal (for example, on zpa_town the human can win by capturing a point before the zombies do).
Currently there are only two maps for ZPA, the two maps being zpa_town and zpa_badbayou.
So far, nobody seems to know what the A in ZPA stands for. The community has jokingly suggested that it is an acronym for Zebra Panda Alliance.