Castling, En Passant and Promotion: Chess's Special Moves

Most chess moves follow the simple rules of each piece. Three do not: castling, en passant and promotion. They come up in almost every game, and they are behind many arguments between new players - so here is exactly how each one works.

Castling

Castling is the only move in chess where you move two pieces at once: the king and one rook. The king moves two squares towards the rook, and the rook jumps over to the square right next to the king, on the other side.

• Kingside castling (short castling), written O-O: the white king goes from e1 to g1 and the rook from h1 to f1.
• Queenside castling (long castling), written O-O-O: the king goes from e1 to c1 and the rook from a1 to d1.

Moves: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. O-O

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Castling does two jobs in one move: it takes the king away from the centre, where the fighting happens, and it brings a rook towards the middle, where it can join the game.

When you are allowed to castle

All of these must be true:

1. Neither the king nor that rook has moved earlier in the game - even if it moved back to its starting square.
2. No pieces stand between the king and the rook.
3. The king is not in check. You cannot castle out of check.
4. The king does not pass through or land on a square that is attacked.

Two things people often get wrong: the rook may be under attack, and when castling queenside the rook may pass over an attacked square (b1 for White) - only the king's path matters. And moving the king loses the right to castle on both sides for the rest of the game.

To castle in a tournament game, move the king first. Touching the rook first can count as a rook move.

En passant

En passant ("in passing" in French) is a special pawn capture. It exists because of the pawn's two-square first move.

When a pawn moves forward two squares from its starting square and lands right beside an enemy pawn, that enemy pawn may capture it as if it had moved only one square. The capturing pawn moves diagonally to the square the other pawn skipped over.

Moves: 1. e4 Nf6 2. e5 d5 3. exd6

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The rules:

• Only a pawn can capture en passant, and only a pawn that has just moved two squares.
• The capturing pawn must be on its fifth rank (the fourth rank for Black).
• It must be done on the very next move. If you play anything else, the chance is gone.

Why does it exist? When the two-square first move was added to the rules in the late Middle Ages, it let a pawn slip past an enemy pawn that would otherwise have been able to capture it. En passant keeps that capture possible.

In notation it is written like a normal pawn capture - exd6 here - sometimes with "e.p." after it.

Promotion

When a pawn reaches the far side of the board (the 8th rank for White, the 1st for Black), it must immediately be promoted: replaced by a queen, rook, bishop or knight of the same colour. You choose - and you can promote even if you still have your original queen, so it is possible to have two or more queens.

Moves: 1. b8=Q

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Most of the time you choose a queen, because it is the strongest piece. That is why the hardest part of many endgames is stopping a pawn from queening.

Underpromotion

Choosing a rook, bishop or knight is called underpromotion. It is rare, but it wins games in two situations:

• A knight gives check or a fork that a queen could not.
• A queen would give stalemate, while a rook or bishop keeps the game going.

Moves: 1. d8=N+ Ke7 2. Nxb7

Open this position on the analysis board

Try spotting these yourself in our underpromotion puzzles: each one is a real game where only the "wrong" piece wins.

Quick summary

Want the rest of the rules? See how to play chess, and how a game can end in a draw.