Move the king two squares, then bring the rook beside it
Castling is a single move involving the king and one rook. In standard chess, White castles kingside by moving the king from e1 to g1 and the rook from h1 to f1. Queenside castling puts the king on c1 and the a1 rook on d1.
Black uses the same files on rank 8: king to g8 and rook to f8, or king to c8 and rook to d8. The notation is O-O for kingside and O-O-O for queenside. In a physical game, move the king first. Chess960 uses different starting arrangements; this lesson covers standard chess.
White retains both castling rights. O-O places the king on g1 and rook on f1.
Position FEN
4k3/8/8/8/8/8/8/R3K2R w KQ - 0 1Check four requirements before castling
Castling is legal only when all the requirements hold. The king and the chosen rook must never have moved. Every square between them must be empty. The king cannot currently be in check. The squares the king crosses and lands on cannot be attacked.
Returning a king or rook to its starting square does not restore castling rights. Moving one rook removes only that rook’s side of the right; moving the king removes both. A promoted rook cannot replace a rook that has lost the right.
This is why a board picture alone cannot prove that castling is available. Piece placement shows the path, but you also need to know the relevant move history.
Queenside castling has one easily missed distinction
For White to castle queenside, b1, c1, and d1 must be empty. The king’s squares e1, d1, and c1 must be safe. The square b1 must be empty, but it does not have to be safe: the king never crosses it.
In the second diagram, a black rook attacks b1. White may still play O-O-O because e1, d1, and c1 are safe and the full path is clear. Similarly, an attack on the castling rook itself does not automatically forbid the move. It is the king’s safety along its route that matters.
The attack on b1 does not stop White from castling queenside.
Position FEN
1r2k3/8/8/8/8/8/8/R3K3 w Q - 0 1Pause at any move in a diagram, then open that exact position in Chat to ask about it or in Coach to practice.
Can you castle out of, through, or into check?
No to all three. A safe destination does not let you castle out of an existing check, and an attack on the crossing square prevents castling even if the destination is safe. For White’s kingside castle, inspect e1, f1, and g1.
Practice by comparing the squares that must be empty with the squares that must be safe. They are related but not identical lists. If a game will not let you castle, use the separate troubleshooting guide to check rights, blockers, and attacked squares in order.
Finally, legal does not always mean wise. Castling toward an active enemy attack may be a poor choice. Learn the rule first, then judge whether the resulting king position actually improves your game.
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Sources and editorial notes
Examples are composed for teaching unless stated otherwise. Legal replay is checked with chess.js; this does not prove that every composed position arose in a real game. Demonstration lines illustrate an idea and are not claimed to be the unique best defense.
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