The queen is the most powerful piece in the game of chess. Each player starts the game with one queen, placed in the middle of his first rank next to his king. Beginners often accidentally interchange the placement of the queen and king, thus the mnemonic "queen on her color". The white queen starts on a white square, and the black queen on a black square. In algebraic notation, the white queen starts on d1 and the black queen on d8.
The queen can be moved in a straight line vertically, horizontally, or diagonally, any number of unoccupied squares as shown to the left, thus combining the moves of the rook and bishop. As with most pieces, the queen captures by occupying the square on which an enemy piece sits.
Ordinarily the queen is slightly more powerful than a rook and a bishop, while slightly less powerful than two rooks. Because the queen is more valuable than any other piece, it is almost always disadvantageous to exchange the queen for a piece other than the enemy's queen.
The queen is at her most powerful when the board is open, when the enemy king is not well-defended, or when there are loose (i.e. undefended) pieces in the enemy camp. Because of her long range and ability to move in more than one direction, the queen is well-equipped to execute forks, but such forks are only useful when both the forked pieces are undefended, or one is undefended and the other is the enemy king.
Beginners often develop the queen as soon as possible, in the hopes of plundering the enemy position and possibly even delivering an early checkmate. While effective against other beginners, this strategy is disadvantageous against experienced players. The defender need only look to his king's safety and make sure every piece is protected, and the attacking queen will not be able to strike home. Moreover, because the queen is too valuable to exchange, the defender can often gain time and space by threatening an exposed queen and forcing her to retreat.
Typically an exchange of queens marks the beginning of the endgame. After the queens and a few other pieces have been exchanged, the kings are able to participate more actively in events, and the focus of the game shifts to a struggle to promote a pawn, usually to a new queen. However, it is not necessary to lose one's queen before gaining a new one by promotion.
See also: Eight queens puzzle.