Castling: the king goes behind a wall of pawns and a rook comes towards the middle, both in one move.
Why it matters
Castling does two jobs in one move: it tucks the king behind a wall of pawns and brings a rook towards the middle. There is no other move in chess that does that much.
The reason it matters so early is that the centre opens without asking. A king still on e1 or e8 when the e-file opens is not a slight problem; it is usually the whole game.
See it on a board
Both kings are behind three untouched pawns and both rooks have joined the game. This is what the opening is for.
Checked: the position really has the feature described.
How to play it
- Clear the two or three squares between the king and rook, then castle — usually by move ten.
- Prefer the side where your pawns are still intact.
- After castling, leave those pawns alone unless you have a reason. Every pawn move in front of the king is a hole you cannot fill again.
At each level
The same idea, said the way it is taught at each age.
Pawn · ages 3–6
Castle early. Your king goes behind the pawns and your rook comes out. Then leave those three pawns alone.
Knight · ages 4–6
Choose the side to castle by looking at where the position will open. Castling into the opponent's attack is worse than staying in the middle a move longer.
What goes wrong
- Delaying castling to win a pawn, and meeting a check on the open e-file two moves later.
- Pushing the pawns in front of the castled king for no reason, which creates permanent weak squares.
Questions people ask
- Is it ever right not to castle?
- In closed positions where nothing can open, occasionally. But it is a decision to justify, not a default, and most games where a king stays in the middle are lost by that king.