Short answer: to castle, move your king two squares toward a rook, then put that rook on the square the king just crossed. It counts as one move. You can only do it if neither piece has moved, the squares between them are empty, and your king is not in check, does not pass through an attacked square and does not land on one.
Castling is the only move in chess where you move two of your own pieces at once. It does two useful jobs: it tucks the king away from the center, and it brings a rook into the game.
How castling works
Watch the board. White castles on the king's side, then Black castles on the queen's side.
Kingside, the king lands on g1 and the rook on f1. Queenside, the king lands on c8 and the rook on d8.
Kingside castling is the short one. The white king goes from e1 to g1, and the rook from h1 to f1. Black's king goes from e8 to g8, and the rook from h8 to f8.
Queenside castling is the long one. The white king goes from e1 to c1, and the rook from a1 to d1. Black's king goes from e8 to c8, and the rook from a8 to d8.
Either way, the king always moves exactly two squares.
The rules of castling
You may castle only when all of these are true:
- Your king has not moved at any point in the game.
- That rook has not moved.
- No pieces stand between them.
- Your king is not in check right now.
- Your king does not pass through an attacked square.
- Your king does not land on an attacked square.
Here is number 5 in action. Black's rook attacks f1, the square the white king would have to cross, so White cannot castle kingside for now.
The rook on f3 attacks f1, so the white king cannot pass over it. White cannot castle kingside until that changes.
What does not stop you castling
These surprise people, and children argue about them at every club:
- Your rook can be under attack. Only the king's path matters.
- The rook can cross an attacked square. In queenside castling, the rook passes over b1, and it does not matter if that square is attacked.
- You may have been in check earlier. If your king got out of it without moving, you can still castle later.
Try it
White to play. Castle kingside: pick up the king and move it two squares to the right.
Task: White castles kingside by moving the king from e1 to g1.
When should you castle?
Early, in most games. A simple plan for children is to bring out a knight and a bishop, then castle within the first ten moves or so.
An uncastled king in the center is the most common reason beginners lose quickly. Once the middle of the board opens up, the king gets attacked from every side. Kingside castling is the usual choice because it takes one less piece to clear out of the way.
There is one thing to watch for: after castling, leave the pawns in front of your king alone unless you have a good reason to move them. They are its shelter.
How to do it at a tournament
Move the king first, then the rook, using one hand. If a player touches the rook first, the rules can treat that as a rook move, and the chance to castle is gone. It is a good habit to teach early.
FAQ
Can you castle if you are in check?
No. You have to deal with the check first. If you do that without moving your king, you can castle on a later move.
Can you castle after your king has moved?
No, not for the rest of the game, even if the king goes back to its starting square.
Can you castle with a rook that was attacked?
Yes. The rook may be under attack. The rules only protect the king's path.
Can you castle on both sides?
Each player can castle only once per game, on one side.
How do you write castling down?
O-O means kingside castling and O-O-O means queenside castling.
Is castling always the best move?
No, but it is usually good, and for a beginner it is a very safe habit.
What comes next
Castling is one of three special moves. The others are promotion and en passant. The basics are all in our chess rules for beginners.
A good coach makes habits like this stick. The first lesson is free and one to one, live online. Book the free first lesson