How to Castle in Chess (and When/Why You Should)

Castling is a special move in chess which accomplishes two important goals at the same time. First, it moves your king away from the center file of the chessboard and closer to the corner where, in theory, it will be better protected. Secondly, it moves one of your rooks out of the corner, and onto a center file where it will usually serve a better purpose. While castling was not a component of early versions of chess, it has been a valid move since at least the 15th century.

With all that said, many people are confused about the nuances of how castling works, and altercations will often take place among novice players who are convinced that they fully understand it.

This article discusses the simple steps for knowing how, when, and why you should castle in chess. It assumes that the reader has a basic understanding of chess terminology and how the pieces move.

Difficulty: Easy

Instructions

1. 
   The starting position

   Observe the starting position of the pieces in chess. Neither the king nor the rooks are on ideal squares. The king is centrally located where it will be hard to protect. The rooks are tucked away in the corners where they will have limited mobility. Castling remedies both of those situations in one move.

2. 
   Cleared for castling kingside

   The general idea behind castling is that the king moves two spaces toward one of the rooks, and, as part of the same move, the rook is placed on the opposite side of the king. Before castling can take place, a number of conditions must be met.

3. 
   Cleared for castling queenside

   The first condition is that there cannot be any pieces at all between the king and the rook on whichever side you will be castling on. The two possible sides are referred to as kingside and queenside. It is not possible to say left side and right side since what would be on the left for one player is on the right for the other.

4. 
   Once the king moves you can no longer castle, even if it moves back

   It must be the case that neither the king nor the rook in question may have previously moved. It doesn't matter if you move one or both back to their original starting positions.

5. 
   Once a rook moves, you can no longer castle on that side, even if it moves back

   If the king moved, you can never castle on either side. If one of the rooks moved, but not the king, you cannot castle on the side of the rook that moved, but you can still castle on the other side.

6. 
   The king is currently in check

   You cannot castle if your king is currently in check. You must get out of check by some other means. If your only choice is to move the king, you will never be able to castle.

7. 
   Castling would move the king through check

   You cannot castle if doing do would move your king through check. Remember that a castling move involves moving the king two spaces toward a rook, and then placing the rook on the other side. Look at the diagram to see an example of castling that would move the king through check, even though it would not end up in check after castling. Such a move is illegal.

8. 
   Castling would move the king into check

   You cannot castle if doing so would move your king such that it ends up in check. Look at the diagram to see an example of this.

9. 
   The rook is under attack. Castling is OK.

   It is OK to castle if your rook is under attack, as long as you are not also violating one of the above rules.

10. 
    The black rook does not impede a queenside castle.

    It is OK to castle if your rook would "pass through" a square that is under attack. The rook is not really passing through any square at all. The king moves two spaces toward a rook, and then as part of that same move, the rook is immediately placed on the opposite side of the king.

11. 
    A completed kingside castle

    Here is an example of a completed kingside castle. In algebraic notation, such a move is denoted O-O.

12. 
    A completed queenside castle

    Here is an example of a completed queenside castle. In algebraic notation, such a move is denoted O-O-O.

13. 
    Castling can be done as early as a player's fourth move

    Note that it is possible and fairly common to castle kingside on one's fourth move, after moving the king's pawn, king's knight, and king's bishop out of the way. Sometimes castling is delayed a bit longer while other pieces are developed. Among experienced players it is uncommon for castling to not take place at all, since it is such an important move.
    
    Castling queenside is not as common as kingside. One reason is that doing so requires all of the above, along with moving the queen out of the way which is often discouraged in the early stages of the game. Castling queenside also doesn't move your king as close to the edge of the board as does castling kingside.

14. 
    Protect your king at all costs!

    That's all you need to know about castling. It sounds more complicated than it is. Don't be surprised if some of your supposedly experienced opponents don't fully understand these rules, and get highly defensive when you try to explain that they've been under various misconceptions about castling all this time. ☺

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[klnygaard]

on 5/28/2009 Great explanation and pictures- 5 stars

[firstwriter]

on 5/26/2009 I love playing chess. Thanks for writing about it!