Chess is a two-player strategy board game played on a checkered board with 64 squares arranged in an 8×8 grid. Played by millions of people worldwide, chess is believed to be derived from the Indian game chaturanga sometime before the 7th century. Chaturanga is also the likely ancestor of the East Asian strategy games xiangqi (Chinese chess), janggi (Korean chess), and shogi (Japanese chess). Chess reached Europe by the 9th century, due to the Umayyad conquest of Hispania. The pieces assumed their current properties in Spain in the late 15th century, and the modern rules were standardized in the 19th century.
Play involves no hidden information. Each player begins with 16 pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. Each piece type moves differently, with the most powerful being the queen and the least powerful the pawn. The objective is to checkmate the opponent's king by placing it under an inescapable threat of capture. To this end, a player's pieces are used to attack and capture the opponent's pieces, while supporting one another. During the game, play typically involves exchanging pieces for the opponent's similar pieces, and finding and engineering opportunities to trade advantageously or to get a better position. In addition to checkmate, a player wins the game if the opponent resigns, or, in a timed game, runs out of time. There are also several ways that a game can end in a draw.
The first generally recognized World Chess Champion, Wilhelm Steinitz, claimed his title in 1886. Since 1948, the World Championship has been regulated by the Fédération Internationale des Échecs (FIDE), the game's international governing body. FIDE also awards life-time master titles to skilled players, the highest of which is Grandmaster (GM). Many national chess organizations have a title system of their own. FIDE also organizes the Women's World Championship, the World Junior Championship, the World Senior Championship, the Blitz and Rapid World Championships, and the Chess Olympiad, a popular competition among international teams. FIDE is a member of the International Olympic Committee, which can be considered recognition of chess as a sport. Several national sporting bodies (e.g. the Spanish Consejo Superior de Deportes) also recognize chess as a sport. Chess was included in the 2006 and 2010 Asian Games. There is also a Correspondence Chess World Championship and a World Computer Chess Championship. Online chess has opened amateur and professional competition to a wide and varied group of players.
Since the second half of the 20th century, chess engines have been programmed to play with increasing success, to the point where the strongest programs play at a higher level than the best human players. Since the 1990s, computer analysis has contributed significantly to chess theory, particularly in the endgame. The IBM computer Deep Blue was the first machine to overcome a reigning World Chess Champion in a match when it defeated Garry Kasparov in 1997. The rise of strong chess engines runnable on hand-held devices has led to increasing concern about cheating during tournaments.
There are many variants of chess that utilize different rules, pieces, or boards. One of these, Fischer Random Chess, has gained widespread popularity and official FIDE recognition.
By convention, chess game pieces are divided into white and black sets. Each set consists of 16 pieces: one king, one queen, two rooks, two bishops, two knights, and eight pawns. The pieces are set out as shown in the diagram and photo. The players of the sets are referred to as White and Black, respectively.
The game is played on a square board of eight rows (called ranks, denoted 1 to 8 from bottom to top according to White's perspective) and eight columns (called files, denoted a to h from left to right according to White's perspective). The 64 squares alternate in color and are referred to as light and dark squares. The chessboard is placed with a light square at the right-hand corner nearest to each player. Thus, each queen starts on a square of its own color (the white queen on a light square; the black queen on a dark square).
In competitive games, the colors are allocated by the organizers; in informal games, the colors are usually decided randomly, for example by coin toss, or by one player's concealing a white and black pawn in either hand and having the opponent choose. White moves first, after which players alternate turns, moving one piece per turn (except for castling, when two pieces are moved). A piece is moved to either an unoccupied square or one occupied by an opponent's piece, which is captured and removed from play. With the sole exception of en passant, all pieces capture by moving to the square that the opponent's piece occupies.
Moving is compulsory; it is illegal to skip a turn, even when having to move is detrimental. A player may not make any move that would put or leave the player's own king in check. If the player to move has no legal move, the game is over; the result is either checkmate (a loss for the player with no legal move) if the king is in check, or stalemate (a draw) if the king is not.
Each piece has its own way of moving. In the diagrams, the dots mark the squares to which the piece can move if there are no intervening piece(s) of either color (except the knight, which leaps over any intervening pieces).
The king moves one square in any direction. The king also has a special move called castling that involves also moving a rook.
A rook can move any number of squares along a rank or file, but cannot leap over other pieces. Along with the king, a rook is involved during the king's castling move.
A bishop can move any number of squares diagonally, but cannot leap over other pieces.
The queen combines the power of a rook and bishop and can move any number of squares along a rank, file, or diagonal, but cannot leap over other pieces.
A knight moves to any of the closest squares that are not on the same rank, file, or diagonal. (Thus the move forms an "L"-shape: two squares vertically and one square horizontally, or two squares horizontally and one square vertically.) The knight is the only piece that can leap over other pieces.
A pawn can move forward to the unoccupied square immediately in front of it on the same file, or on its first move it can advance two squares along the same file, provided both squares are unoccupied (black dots in the diagram); or the pawn can capture an opponent's piece on a square diagonally in front of it on an adjacent file, by moving to that square (black "x"s). A pawn has two special moves: the en passant capture and promotion.