Chess is played on a chessboard, a square board divided into 64 squares (eight-by-eight) of alternating color. Lighter-colored squares are called "light" or "white", and the darker-colored squares are called "dark" or "black".
The board is placed so that a white square is in each player’s near-right corner. Each player controls sixteen pieces:
At the beginning of the game, the pieces are arranged as shown in the diagram to the right.
Each square of the chessboard is identified with a unique pair of a letter and a number. The vertical files are labeled a through h, from White’s left to White’s right. Similarly, the horizontal ranks are numbered from 1 to 8, starting from the one nearest White’s side of the board. Each square of the board, then, is uniquely identified by its file letter and rank number. The white king, for example, starts the game on square e1.
White moves first and the players alternate moves.
Making a move is mandatory; it is not legal to "pass”.
Play continues until a king is checkmated, a player resigns, or a draw is declared.
Moves are made to vacant squares except when capturing an opponent’s piece.
With the exception of the knight, pieces cannot jump over each other.
When a piece is captured (or taken), the attacking piece replaces the enemy piece on its square (en passant being the only exception). The captured piece is removed from the game and may not be returned to play for the remainder of the game. The king cannot be captured.
The king can move exactly one square horizontally, vertically, or diagonally.
Each king is allowed to make a special move, known as castling (see below)
The rook moves any number of vacant squares vertically or horizontally.
The bishop moves any number of vacant squares in any diagonal direction.
The queen can move any number of vacant squares diagonally, horizontally, or vertically.
The knight can jump over pieces. The knight moves in an "L" shape. Two steps one direction, a 90° turn, and one step in the new direction.
pawns can move forward one square, if that square is unoccupied. If it has not yet moved, the pawn has the option of moving two squares provided both squares in front of the pawn are unoccupied.
A pawn cannot move backward.
Pawns are the only pieces that capture differently from how they move. They can capture an enemy piece on the two squares diagonally in front of them. but cannot move to these spaces if they are vacant.
The pawn is also involved in the two special moves en passant and promotion (see below)
Castling consists of moving the king two squares towards a rook, then placing the rook on the other side of the king.
Castling is only permissible if all of the following conditions are true:
- The king and rook involved in castling must not have previously moved.
- There must be no pieces between the king and the rook.
The king may not currently be in check, nor pass through or end up in check.
If player A’s pawn moves forward two squares and player B has a pawn on the fifth rank and on an adjacent file, B’s pawn can capture A’s pawn as if A’s pawn had only moved one square. This capture can only be made on the immediately subsequent move. In this example, if the white pawn moves from a2 to a4, the black pawn on b4 can capture it en passant and move to a3.
If a pawn advances to its eighth rank, it is then promoted (converted) to a queen, rook, bishop, or knight of the same color, the choice being at the discretion of its player.
When a player makes a move that threatens the opposing king with capture, the king is said to be in check.
If a player’s king is in check then the player must make a move that eliminates the threat(s) of capture.
A player may never leave their king in check at the end of their move.
In informal games, it is customary to announce check when making a move that puts the opponent’s king in check.
A player may not make any move which places or leaves their king in check.
If a player’s king is placed in check and there is no legal move that player can make to escape check, then the king is said to be checkmated, the game ends, and that player loses
The diagram to the right shows a typical checkmate position. The white king is threatened by the black queen; every square to which the king could move is also threatened; it cannot capture the queen, because it would then be threatened by the rook.
Either player may resign at any time and their opponent wins the game. This normally happens when the player believes he or she is very likely to lose the game.
The game ends in a draw if any of these conditions occur:
- The player to move is not in check but has no legal move. This situation is called a stalemate. An example of such a position is shown in the diagram to the right.
- There is insufficient material, for example if one player has a king and a bishop or knight and the other only a king.
- Both players agree to a draw after one of the players makes such an offer.
The player having the move may claim a draw by declaring that one of the following conditions exists, or by declaring an intention to make a move which will bring about one of these conditions:
Fifty moves have been played by each player without any capture or a pawn being moved.
The same board position has occurred three times.