Enemy Territory was originally planned to be released as a commercial expansion pack to the popular FPS Return to Castle Wolfenstein. However, due to problems with the single-player aspect, the multiplayer portion was released on May 29, 2003 as a free standalone game. In early 2004 the source code for the game logic (not the game engine) was released to the benefit of its modding community.

There are two sides, Allies and Axis. There are six officially released maps, and many community-created maps. On each map, the offense needs to complete a certain set of objectives within a limited amount of time. The defense needs to keep the offense from completing objectives until time runs out. Some objectives may be optional, and some objectives can be carried out by either team. These minor objectives assist the team completing them. Depending on Game Mode the action will continue on another map (Campaign Mode) or the same map (Objective Mode, Stopwatch Mode, Last Man Standing).

In the official six-map campaign (most common on public servers), Allies are offense for all but one map. In Stopwatch Mode (most common for locked or LAN servers) two teams - most common setups: 6vs6 or 3vs3 - will play the same map twice, once in each side and the winner is determined of who have the fastest offence (it can be a tie when both teams defence manage to keep the offence from completing the objectives until time runs out).

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