Correspondence chess

The International Correspondence Chess Federation, ICCF, defines correspondence chess as a game in which the players do not sit opposite each other at the same chessboard and instead transmit their moves remotely. Historically this could be done by post; today much organized correspondence play is conducted through dedicated servers.

The defining feature is not merely the use of the internet, but the delayed-response format. Rules that determine how much time each player has to move allow much longer reflection than a normal in-person game, and a player may have several games in progress at once. The exact transmission and timing rules depend on the competition.

What ICCF rules permit

In competitions governed by ICCF, a player must decide the move personally but may consult publicly available information, including books, game databases, and chess engines, computer programs that analyze positions and calculate variations. That permission belongs to ICCF rules and should not be assumed for other forms of chess.

Postal chess is a historical and still recognizable form of correspondence chess in which moves are sent through physical mail. Online chess is a broader concept: a five-minute game on a website is online, but that does not make it correspondence chess. Compared with over-the-board chess, the fundamental difference is that the opponents do not share the same physical board when making their moves.