Castling
Castling is a special type of chess move. When castling, you simultaneously move your king, and one of your rooks. The king moves two squares towards a rook, and that rook moves to the square at the other side of the king, to the square over which the king crossed.
Castling is the only move in chess in which a player moves two pieces in the same move, and it is the only move aside from the knight's move where a piece can be said to "jump over" another.
Castling is technically a king move.
Castling is permissible if and only if all of the following conditions hold:
The king and the chosen rook are on the player's first rank.
Neither the king nor the chosen rook has previously moved.
There are no pieces between the king and the chosen rook.
The king is not currently in check.
The king does not pass through a square that is attacked by an enemy piece.
The king does not end up in check. (True of any legal move.)
Conditions 4 through 6 can be summarized with the more memorable phrase: "One may not castle out of, through, or into check."
There are several common misconceptions about Castling. To clarify:
The chosen rook may be under attack.
The rook may move through an attacked square, provided the king does not. The only such square is the one adjacent to the rook, when castling queenside.
The king may have been in check earlier in the game (provided the king did not move when resolving the check).
In handicap games where odds of a rook are given, the player giving odds may still castle with the absent rook, moving only the king.
Kingside or Short Castling
Queenside or Long Castling
Castling in Variations of Chess, perhaps with different shapes and sizes of boards? How is it affected?
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