Castling is the only move in which the king and a rook move together. The king moves two squares towards the rook, and the rook jumps over the king to the square right next to it. Castling has two goals: to take the king away from the centre to a safe corner behind its pawns, and to bring the cornered rook into play.
Short and long castling
- Short castling (O-O) is on the kingside: the white king goes from e1 to g1 and the h1 rook to f1.
- Long castling (O-O-O) is on the queenside: the white king goes from e1 to c1 and the a1 rook to d1.
- Black castles the same way on the eighth rank: the king goes to g8 (short) or c8 (long).
When you cannot castle
- The king has already moved (even if it returned): no more castling for the rest of the game.
- The rook involved has already moved: no castling on that side.
- There is any piece between the king and the rook.
- The king is in check: you cannot castle out of check.
- The square the king passes over or lands on is attacked by the opponent.
A common question: can you castle if the rook is attacked, or if b1 is attacked during long castling? Yes. The rule only concerns the squares the king crosses and lands on; the rook's safety and the b1/b8 square the king does not cross do not matter.
How to castle over the board
In official games you should move the king two squares first and then place the rook with the same hand. If you touch the rook first, the arbiter may apply the touch-move rule and require a rook move. Short castling is written O-O and long castling O-O-O.
When should you castle?
The general principle is to develop your knights and bishops and castle early, usually within the first ten moves. Leaving the king on e1/e8 while central files open invites a direct attack. Long castling leads to sharper play: the king is slightly more exposed, but the rook lands immediately on the central d-file. Opposite-side castling usually means mutual pawn storms and fast attacks.
Common castling mistakes
- Postponing castling because 'I'm fine' and then losing the king on open central files.
- Pushing the pawns in front of the castled king without need and weakening it.
- Planning your attack without noticing which side your opponent will castle to.
💡 If your opponent's king is stuck in the centre and you have castled, opening the centre with pawn trades usually favours you. If your own king is in the centre, keep the centre closed.