Castling in Chess

Castling is a special move in chess that lets you do two important things at once: move your king to safety and activate your rook. It is the only move in chess where two pieces move at the same time.

Types of Castling

Kingside Castling (O-O)

The king moves two squares toward the h-file rook, and the rook jumps over to the other side of the king.

  • King: e1 → g1 (White) or e8 → g8 (Black)
  • Rook: h1 → f1 (White) or h8 → f8 (Black)

Queenside Castling (O-O-O)

The king moves two squares toward the a-file rook, and the rook jumps to the other side of the king.

  • King: e1 → c1 (White) or e8 → c8 (Black)
  • Rook: a1 → d1 (White) or a8 → d8 (Black)

Requirements for Castling

All of these conditions must be met to castle:

  1. The king has not previously moved in the game.
  2. The rook involved has not previously moved in the game.
  3. There are no pieces between the king and the rook.
  4. The king is not currently in check.
  5. The king does not pass through a square that is attacked by an enemy piece.
  6. The king does not land on a square that is attacked by an enemy piece.

When to Castle

  • Castle early, usually within the first 10 moves. An uncastled king in the center is vulnerable to attacks.
  • Kingside castling (O-O) is more common and usually safer because the king is tucked behind more pawns.
  • Queenside castling (O-O-O) can be aggressive. The rook immediately lands on the d-file, often an open or semi-open file.
  • Don't castle into an attack. If your opponent has aimed pieces at your kingside, consider castling queenside instead.
  • Sometimes it's better not to castle at all, for example in endgames where the king should be active in the center.

Castling Notation

In standard algebraic notation, castling uses the letter O (not the number zero):

  • O-O = Kingside castling
  • O-O-O = Queenside castling

Example game: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O (White castles kingside on move four)

Common Mistakes

  • Moving the king or rook "just one square" early on. This permanently loses the right to castle on that side.
  • Castling into an opponent's pawn storm or piece attack.
  • Forgetting that the king cannot castle through check, even if the destination square is safe.
  • Delaying castling too long and getting caught in a central attack.