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Rules & notation

Castling

The one move where the king and a rook move together, tucking the king to safety.

The king moves two squares toward a rook and that rook hops to the far side. You may castle only if neither piece has moved, the king is not in check, and the king does not pass through or land on an attacked square. Kingside castling is written O-O; queenside is O-O-O.

It is the fastest way to get your king safe and your rook into the game at the same time — usually a priority in the opening.

Why it matters

An uncastled king in the centre is the target of a huge share of attacking games. Castling early avoids most of them.

The mistake everyone makes

Delaying castling to grab a pawn, then getting the king caught in the centre as the position opens.

Related terms

King safety
How exposed your king is to attack — usually the most important factor in the middlegame.
Development
Bringing your pieces off the back rank into active, useful positions.
Opening principles
The starter rules: control the centre, develop pieces, castle early, don't move the queen out too soon.
Luft
An escape square made for the king, usually by advancing a pawn in front of it.

See Castling in your own games

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