Correspondence chess is chess played by some sort of long-distance correspondence, usually through the postal system or e-mail. Less usual methods which have been employed include fax and homing pigeon. It is opposed to so-called over-the-board (OTB) chess, where the players are sat at a chessboard at the same time.
Postal chess allows people or clubs geographically distant to play one another without meeting in person. The length of a game played by correspondence can vary depending on the method used to transmit the moves - a game played by e-mail might last no more than a few months, but a game played by post between players in different countries might last five years or more.
Correspondence chess differs from over-the-board play in several respects. While in OTB chess only one game is played at a time (the exception being in a simultaneous exhibition), in correspondence chess several games are usually played at once. All games in a tournament are played concurrently, and some players may have more than a hundred games continuing at the same time.
The time limits in correspondence play are far longer than over-the-board chess, being measured in weeks and months rather than minutes and hours. This allows for far deeper calculation, meaning that blunders are very rare. The use of chess books and chess computers is allowed, although many hobby players voluntarily do without them. At the top level, however, computers, while useful for checking relatively short-term tactics, are no match for the strongest players if left to play a complete game.
The international governing body of correspondence chess is the International Correspondence Chess Federation (ICCF) which organises postal and e-mail events. There are numerous national and regional bodies for postal chess, as well as a number of organisations devoted to organising e-mail play.
The ICCF awards the titles International Master, Senior International Master and Grandmaster - these are equivalent to similar titles awarded by FIDE for over-the-board chess. The ICCF also runs the World Correspondence Chess Championships. The winner of the 15th Championships, completed in 2002, was Gert Jan Timmerman. As of November 2003 the 16th Championship is incomplete, but T. Hamarat has an unassailable lead. The final of the 17th Championship began in March 2002, and the 18th began in June 2003.
Although nowadays the strongest correspondence players are specialists, not often well known in over-the-board play, a number of notable players in the past have played postal games. Paul Keres, an Estonian sometimes regarded as the strongest player never to become world champion, played many games of correspondence chess, apparently because he had difficulty finding players in his native country anywhere near strong enough to give him a decent game. Alexander Alekhine and Max Euwe also played.