Chess Castling, En Passant & Promotion Rules Explained
Castling, en passant and promotion are the three special move rules most likely to interrupt a first chess game.
Castling
Castling moves the king two squares toward a rook and places that rook on the square the king crossed. It is legal only if the king and the chosen rook have not previously moved, all squares between them are empty, the king is not currently in check, and the king does not cross or finish on a square attacked by an opposing piece.
En passant
If a pawn advances two squares from its starting position and lands beside an opposing pawn, that opposing pawn may capture it as though it had advanced only one square. The en passant capture is available only on the immediately following move.
Promotion
When a pawn reaches the farthest rank, it must be replaced as part of the same move by a queen, rook, bishop or knight of the same color. The chosen piece does not have to be one previously captured, so more than one queen is possible.
Related guides
Complete chess rules · Checkmate and draws · Chess hub