Chess is a two-player strategy board game played on a chessboard, a checkered game board with 64 squares arranged in an eight-by-eight grid.
Once in every game, each king is allowed to make a special move, known as castling. Castling consists of moving the king two squares along the first rank toward a rookand then placing the rook on the last square the king has just crossed.
When a pawn advances two squares from its starting position and there is an opponent’s pawn on an adjacent file next to its destination square, then the opponent’s pawn can capture it en passant (in passing), and move to the square the pawn passed over. However, this can only be done on the very next move, otherwise the right to do so is forfeit.
When a king is under immediate attack by one or two of the opponent’s pieces, it is said to be in check. A response to a check is a legal move if it results in a position where the king is no longer under direct attack (that is, not in check). This can involve capturing the checking piece; interposing a piece between the checking piece and the king (which is possible only if the attacking piece is a queen, rook, or bishop and there is a square between it and the king); or moving the king to a square where it is not under attack.
- Stalemate – the player whose turn it is to move is not in check, but has no legal move.
- Threefold repetition of a position – this most commonly occurs when neither side is able to avoid repeating moves without incurring a disadvantage. The three occurrences of the position need not occur on consecutive moves for a claim to be valid. FIDE rules make no mention of perpetual check; this is merely a specific type of draw by threefold repetition.
- The fifty-move rule – if during the previous 50 moves no pawn has been moved and no capture has been made, either player may claim a draw; this requires the players to keep a valid written record of the game so that the claim may be verified by the arbiter if challenged. There are in fact several known endgames where it is theoretically possible to force a mate but which require more than 50 moves before the pawn move or capture is made; examples include some endgames with two knights against a pawnand some pawnless endgames such as queen against two bishops. These endings are rare, however, and few players study them in detail, so the fifty-move rule is considered practical for over the board play. Some correspondence chess organizations allow exceptions to the fifty-move rule
chess games may also be played with a time control, mostly by club and professional players. If a player’s time runs out before the game is completed, the game is automatically lost (provided his opponent has enough pieces left to deliver checkmate). The duration of a game ranges from long games played up to seven hours to shorter rapid chess games, usually lasting 30 minutes or one hour per game. Even shorter is blitz chess, with a time control of three to 15 minutes for each player, and bullet chess (under three minutes). In tournament play, time is controlled using a game clock that has two displays, one for each player’s remaining time.
Notation for recording moves
Chess games and positions are recorded using a special notation, most often algebraic chess notation. Abbreviated (or short) algebraic notation generally records moves in the format “abbreviation of the piece moved – file where it moved – rank where it moved”. For example, Qg5 means “queen moves to the g-file and 5th rank” (that is, to the square g5). If there are two pieces of the same type that can move to the same square, one more letter or number is added to indicate the file or rank from which the piece moved, e.g. Ngf3 means “knight from the g-file moves to the square f3”. The letter P indicating a pawn is not used, so that e4 means “pawn moves to the square e4”.