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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.

Contents 1 Types 1.1 Timed turns 1.1.1 Partially turn-based 1.1.2 Acting outside one's turn 1.1.3 Special turns 1.1.4 Separate phases within turns 2 Turn-based vs. real-time gameplay 3 See also 4 External links

Turn-based games come in two flavors 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. 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.

Most board 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 benifits 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.

Early Ultima games featured timed turns: they were strictly turn-based, but if the player waited more than a second or so to issue a command, the game would automatically issue a pass command, allowing the monsters to take a turn while the player characters did nothing. Further, many browser-based games allocate a number of turns (usually only one) that can be played within a certain period of time (called a tick). Play continues regardless of any turns/ticks that players may have missed.

Many other games that are not generally turn-based retain the notion of turns during specific sequences. Notably, the role-playing computer game Fallout is turn-based during the combat phase, and real-time throughout the remainder of the game. Other games, such as the Total War series of turn-based strategy games, combine a turn-based strategic layer with real-time tactical (RTT) combat.

Some games—notably, the X-COM series of video games and the board wargame, Advanced Squad Leader—allow players to act outside of their normal turn by providing a means of interrupting an opponent's turn and executing additional actions. Typically, the number and type of actions a player may take during an interrupt sequence is limited by the amount of points remaining in the player's action point pool (or something similar) carried over from the previous turn. The Silent Storm video game series includes an "Interrupt" statistic for each character to determine the likelihood of out-of-turn action. In M.A.X., defensive units may be set to fire out of turn at the expense of being able to fire in their own turn.

In some games, not all turns are alike. Usually, this is difference in what phases (or different portions of the turn) happen. Imperium Romanum II for instance, features a "Taxation and Mobilization Phase" in every third turn (month), which does not occur in the other turns. Napoleon has an unusual variation on the idea, where every third player turn is 'night turn' where combat is not allowed.

The Battle Isle series uses an interesting turn-based system: while turns are sequential, they are split into separate movement and attack phases. I.e., the player issues all the movement orders first, then issues the attack orders in a separate, later phase. The effect of this is that players have to wait until the next turn to move their units into spaces that have been cleared.

Main article: Real-time vs. turn-based gameplay

A debate has emerged between fans of real-time strategy and turn-based strategy (and related genres) based on the merits of the real-time and turn-based systems.

• Tick-based game
• Turn-based strategy
• Turn-based tactics
• Game mechanic

• Time Systems - RogueBasin - describes several types of turn-based systems used in roguelikes