Castling is a chess move that safeguards the king and activates a rook at the same time. It's also the only time in chess when you can move two pieces at once. You may castle on the kingside (right) or on the queenside (left), but the rule is the same: The king moves two squares to the right or left, and the rook slides around the king and occupies the square adjacent to the king, ending up on the king's opposite side.

In both cases, the king moves two squares to the side and the rook slides around to the other side of the king. The correct method of castling involves touching the king first. Technically, if you touch the rook first, you must move that piece and only it. Avoid fights and always castle by moving the king first! (Chess is a game full of etiquette.)

Now that you know what castling looks like, you need to be aware that this move isn't always legal. Many a complaint has been made regarding this technicality!

You can't castle in any of the following situations:

• If another piece is between the king and rook.
• If the king has already moved.
• If the rook has already moved (however, you may be able to castle by using the other rook).
• When in check.
• If the king must pass through a square controlled by the opponent. You can't castle through check.

You can castle even if any of the following are true:

• The rook is under attack.
• The rook (but not the king) must pass though a square controlled by the opponent.