The queen is the most powerful piece in the game of chess, able to move any number of squares vertically, horizontally, or diagonally. Each player starts the game with one queen, placed in the middle of the first rank next to the king
The queen can be moved any number of unoccupied squares in a straight line vertically, horizontally, or diagonally, thus combining the moves of the rook and bishop. The queen captures by occupying the square on which an enemy piece sits.
Although both players start with one queen each, a player can promote a pawn to any of several types of pieces, including a queen, when the pawn is moved to the player's furthest rank (the opponents first rank). Such a queen created by promotion can be an additional queen, or if the player's queen has been captured, a replacement queen. Pawn promotion to a queen is colloquially called queening which is by far the most common type of piece a pawn is promoted to because of the relative power of a queen
Ordinarily the queen is slightly more powerful than a rook and a bishop together, while slightly less powerful than two rooks. It is almost always disadvantageous to exchange the queen for a single piece other than the enemy's queen.
The reason the queen is more powerful than a combination of a rook and bishop, even though they control the same number of squares, is twofold. First, the queen is a more mobile unit than the rook and bishop, as the entire power of the queen can be transferred to another location in one move, while transferring the entire firepower of a rook and bishop requires two moves. Second, the queen is not hampered by the bishop's inability to control squares of the opposite color to the square on which it stands. A factor in favor of the rook and bishop is that they can attack (or defend) a square twice, while a queen can only do so only once, but experience has shown that this factor is usually less significant than the points favoring the 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 multiple directions, the queen is well-equipped to execute forks. Compared to other long range pieces (i.e. rooks and bishops) the queen is less restricted and more powerful also in closed positions