Correspondence chess is chess played by various forms of long-distance correspondence, traditionally through the postal system. Today it is usually played through a correspondence chess server, a public internet chess forum, or email. Less common methods that have been employed include fax, homing pigeon and phone. It is in contrast to over-the-board (OTB) chess, where the players sit at a physical chessboard at the same time; and most online chess, where the players play each other in real time over the internet. However, correspondence chess can also be played online.

Correspondence chess allows people or clubs who are 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 moves: a game played via a server or by email might last no more than a few days, weeks, or months; a game played by post between players in different countries might last several years.

Correspondence chess differs from over-the-board (OTB) play in several respects. While players in OTB chess generally play one game at a time (an exception being a simultaneous exhibition), correspondence players often have several games going at once. Tournament games are played concurrently, and some players may have more than one hundred games continuing at the same time.

Time limit in correspondence game is not rigidly defined, but it is generally accepted that, on average, it is never less than one day per move (not counting transmission time in postal chess). This time allows for far deeper calculation, meaning that blunders can be less frequent. A high-level correspondence game can last over a year.

Certain forms of assistance, including books and chess databases, are often allowed; organizations vary as to whether chess engine use is permitted.

Computer assistance has altered correspondence chess. The decline in the popularity of traditional postal correspondence chess occurred at the end of the 20th century. This is also when chess programs became widely accessible, and their playing strength soon reached the level of grandmasters. Due to correspondence chess being played remotely, it is difficult to verify or regulate engine usage, which has led some organizations to simply allow it instead. This is in contrast to over-the-board chess competitions, where all chess organizations strictly prohibit the use of any electronic devices .

The International Correspondence Chess Federation (ICCF), the only correspondence chess organization affiliated with FIDE, the international chess organization, allows for collaboration between humans and computers, even during the World Correspondence Chess Championship. It also allows the use of reference materials that provide the best move in a given position, such as endgame tablebases. The ICCF calls this a "hybrid competition that involves the strategy and planning of humans guided by the accuracy of machines". Due to the accuracy and defensive abilities of modern engines, the draw rate of correspondence games is very high compared to over-the-board chess games.

In contrast, Chess.com's Daily Chess strictly prohibits the use of chess engines and all winners' games are subject to computer analysis for fair play. A similar stance is taken by the United States Chess Federation, which also explicitly prohibits the use of "chess playing algorithms" for evaluating games.