Chess is a two-player board game played on a chessboard, a square checkered board with 64 squares arranged in an 8x8 grid. It is one of the world's most popular games, played by millions of people worldwide.
White always moves first. After the initial move, the players alternately move one piece at a time (with the exception of castling, when two pieces are moved). Pieces are 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 opponent's pieces by moving to the square that the opponent's piece occupies. A player may not make any move that would put or leave his king under attack. If the player to move has no legal moves, the game is over; it is either a checkmate (if the king is under attack) or a stalemate.
Each chess piece has its own style of moving:
The king moves one square in any direction. The king can also castle, a move which requires the rook.
The rook can move any number of squares along any rank or file, but may not leap over other pieces. The rook is also involved during the king's castling move.
The bishop can move any number of squares diagonally, but may not leap over other pieces.
The queen combines the power of the rook and bishop and can move any number of squares along rank, file, or diagonal, but it may not leap over other pieces.
The 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.
The pawn may move forward to the unoccupied square immediately in front of it on the same file; or on its first move it may advance two squares along the same file, provided both squares are unoccupied; or it may move to a square occupied by an opponent's piece which is diagonally in front of it on an adjacent file, capturing that piece. The pawn has two special moves: the en passant capture and pawn promotion.