A turn-based game is a game where the game flow is partitioned into well-defined and visible parts, called turns or rounds. For example, when the game flow unit is time, turns represent units of time, like years, months, weeks, or days. A player of a turn-based game is allowed a period of analysis (sometimes bounded, sometimes unbounded) before committing to a game action, ensuring a separation between the game flow and the thinking process, which in turn presumably leads to more optimal choices. Once every player has taken his or her turn, that round of play is over, and any special shared processing is done. This is followed by the next round of play. The opposite of turn-based is called real-time.

The term turn-based gaming can also be used to refer to browser-based gaming sites that allow for game-play to extend beyond a single session, over long periods of time—often taking months for complex games like Go or Chess to finish.

Types

Turn-based games come in two main forms depending on whether, within a turn, players play simultaneously or take their turns in sequence. The former games fall under the category of simultaneously-executed games (also called phase-based or "We-Go"), with Diplomacy being a notable example of this style of game. The latter games fall into player-alternated games (also called "I-Go-You-Go", or "IGOUGO" for short), and are subsequently subdivided into (A) ranked, (B) round-robin start, (C) random and (D) initiative-based -- the difference being the order under which players start within a turn: (A) the first player being the same every time, (B) the first player selection policy is round-robin, (C) the first player is randomly selected, and (D) the first player is selected based on a separately calculated initiative score.

Timed turns

Most board games and Play-by-mail games are turn-based, providing each player with an opportunity to act. Many single-player strategic video games are also turn-based. However, when a particular player gains access to the game during his/her turn it is not uncommon to limit the time taken by the player to make the move in order to improve the fairness of the game (and to place an upper limit on the game length). In chess, a pair of stop clocks may be used to track the time taken by players to make their moves. This adds many of the benefits of real-time games.

Exchange Chess is an extreme example of this system. Exchange Chess is a four player game played on two boards with each team taking one white and one black side. Any taken piece is given to a teammate, and can be placed on his board as a standard move (in any position that does not put his opponent in check). One viable strategy is to gain a temporary material advantage, pass it on to a teammate, and then stop playing on one's own board—thereby allowing the teammate to use the advantage for many future moves on his board. To avoid this, players are often limited to ten seconds per move—with their opponent being allowed to remove one of the player's pawns from the board for each ten seconds taken.