How do you castle in chess?

Castling in chess is a unique move that can only be performed once per game by each player. It requires a very specific set of conditions, but it is useful. It involves the king and either rook switching places to put the rook into better position to move or to protect the king.

1. Ensure that castling is legal in the game

   The conditions to castle are as follows: first, neither the king nor the king's/queen's rook can have made any prior moves; second, there cannot be a piece between the two; finally, the king cannot be in check at the time of castling, nor can it move into or through check. If any of these are not true, the player cannot castle with that rook. The queen's rook is also available to castle.

2. Move the king

   The king moves two squares to the right or left from the player's perspective to rest on the knight or queen's bishop square. It's important to do this first because it indicates castling; moving the rook is a valid move on its own and concludes the move in tournament play.

3. Move the rook

   After the king has been placed, move the rook to the square on the other side of the king.