The King is the most important piece. When he is trapped, his whole army loses. The King can move one square in any direction — for example, to any of the squares with dots in this diagram. (An exception is castling, which is explained later.) The King may never move into check — that is, onto a square attacked by an opponent's piece.

The pawn moves straight ahead (never backward), but it captures diagonally. It moves one square at a time, but on its first move it has the option of moving forward one or two squares. In the diagram, the squares with dots indicate possible destinations for the pawns. The White pawn is on its original square, so it may move ahead either one or two squares. The Black pawn has already moved, so it may move ahead only one square at a time. The squares on which these pawns may capture are indicated by an X.

If a pawn advances all the way to the opposite end of the board, it is immediately "promoted" to another piece, usually a Queen. It may not remain a pawn or become a King. Therefore, it is possible for each player to have more than one Queen or more than two Rooks, Bishops, or Knights on the board at the same time.