Game Setup

Chess is played on a square board of eight rows (called ranks and denoted with numbers 1 to 8) and eight columns (called files and denoted with letters a to h) of squares. The colors of the sixty-four squares alternate and are referred to as "light squares" and "dark squares". The chessboard is placed with a light square at the right hand end of the rank nearest to each player, and the pieces are set out as shown in the diagram, with each queen on its own color.

The pieces are divided, by convention, into white and black sets. The players are referred to as White and Black, and each begins the game with sixteen pieces of the specified color. These consist of one king, one queen, two rooks, two bishops, two knights and eight pawns. White moves first. The players alternate moving one piece at a time (with the exception of castling, when two pieces are moved simultaneously). Pieces are moved to either an unoccupied square, or one occupied by an opponent's piece, capturing it and removing it from play. With one exception (en passant), all pieces capture opponent's pieces by moving to the square that the opponent's piece occupies.

When a king is under immediate attack by one or two of the opponent's pieces, it is said to be in check. The only permissible responses to a check are to capture the checking piece, interpose a piece between the checking piece and the king, or move the king to a square where it is not under attack. Castling is not a permissible response to a check. A move that would place the moving player's king in check is illegal. The object of the game is to checkmate the opponent; this occurs when the opponent's king is in check, and there is no way to remove it from attack.

Moves

Each chess piece has its own style of moving. The X's mark the squares where the piece can move if no other pieces (including one's own piece) are on the X's between the piece's initial position and its destination. If there is an opponent's piece at the destination square, then the moving piece can capture the opponent's piece. The only exception is the pawn which can only capture pieces diagonally forward.

Special moves

Castling

Once in every game, each king is allowed to make a special move, known as castling. Castling consists of moving the king two squares towards a rook, then placing the rook immediately on the far side of the king. Castling is only permissible if all of the following conditions hold:

• Neither of the pieces involved in the castling may have been previously moved during the game;
• There must be no pieces between the king and the rook;
• The king may not currently be in check, nor may the king pass through squares that are under attack by enemy pieces. As with any move, castling is illegal if it would place the king in check.
• The king and the rook must be on the same rank (to exclude castling with a promoted pawn, described later).

En passant

When a pawn advances two squares, if there is an opponent's pawn on an adjacent file next to its destination square, then the opponent's pawn can capture it and move to the square the pawn passed over, but only on the next move. For example, if the black pawn has just advanced two squares from f7 to f5, then the white pawn on e5 can take it via en passant on f6.

Promotion

When a pawn advances to its eighth rank, it is exchanged for the player's choice of a queen, rook, bishop, or knight of the same color. Usually, the pawn is chosen to be promoted to a queen, but in some cases another piece is chosen, called underpromotion. In the diagram on the right, the pawn on c7 can choose to advance to the eighth rank to promote to a better piece.

End of the game

Chess games do not have to end in checkmate — either player may resign if the situation looks hopeless. If it is a timed game a player may run out of time and lose, even with a much superior position. Games also may end in a draw (tie). A draw can occur in several situations, including draw by agreement, stalemate, threefold repetition of a position, the fifty-move rule, or a draw by impossibility of checkmate (usually because of insufficient material to checkmate).

Time control

Besides casual games without exact timing, chess is also 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 timing ranges from long games played up to seven hours to shorter games lasting usually 30 minutes or one hour per game. Even shorter is blitz chess with a time control of three to fifteen minutes for each player, or bullet chess (under three minutes).

Source: Wikipedia.org