Capture the flag is a traditional outdoor game often played by children where two teams have a flag each and the objective is to capture the other team's flag, located at the team's "base", and bring it back to their own base. It is also a popular paintball game.

One variation of the game includes a "jail" area in addition to the flag on each team's territory. If a member of one team gets tagged by a member of the second team in the second team's territory, the tagged person must sit in jail either for a pre-determined time limit, or until an untagged member runs through the jail.

Software/games

In 1995, Richard Carr released a MS-DOS based game called Capture the Flag. It is a turn based strategy game with real time network / modem play (or play-by-mail) based around the traditional outdoor game.

A similar gameplay, often called CTF, is found in many first-person shooters such as Quake, Unreal Tournament, and Tribes. The teams have their flag and the players attempt to take the enemy's flag from their base and bring it back to their own flag to score. CTF is most commonly played in multiplayer games.

CTF was first introduced as a modification to Quake by the company Threewave. CTF is also a popular mode in the Team Fortress and Team Fortress Classic mods for Quake and Half-Life respectively.

Halo: Combat Evolved for the Xbox includes two CTF variants: CTF Pro and Invasion. In CTF Pro, both flags need to be at the same location for a score, requiring that a team's flag remain protected in home base. In the Invasion scenario, a team starts with the enemy's flag and must deliver it to the enemy base.

Compared to a deathmatch game, CTF scenarios often feature some sort of transportation tool that can be used to travel faster and to reach areas which the player wouldn't normally be able to reach without this extra aid. Such tools might be a grappling hook (aka ninja rope) or a portable teleporter. In Battlefield 1942 CTF the many vehicles available in the game serve this role.

Computer security

In computer security, capture the flag (CTF) is an information warfare game. Each team is given a machine (or small network) to defend on an isolated network. Teams are scored on both their success in defending their assigned machine and on their success in attacking other team's machines. Depending on the nature of the particular CTF game, teams may either be attempting to take an opponent's flag from their machine or teams may be attempting to plant their own flag on their opponent's machine. CTF was popularized by the hacker conference DEF CON.

CTF is often used as an educational exercise to give participants experience in securing a machine, as well as in conducting and reacting to real attacks using commonly available tools, in order to demonstrate the level of effectiveness of their chosen defensive strategies and tools.