Castling is a special move in Chess that involves two pieces at once: the king and one of the rooks. The move exchanges the order of the two pieces on the back rank as if they jumped over each other.

Castling is performed in the following way: the king moves two squares towards the rook, and the rook jumps over the king and moves to the adjacent field (to the field which the king has crossed). It has two types depending on the rook:

• Castling with the nearer rook is called short or kingside castling. In that case both pieces move two fields towards each other.
• Castling with the farther rook is called long or queenside castling. In that case the rook moves three, and the king moves two fields.

White castling short

White castling long

Black castling short

Black castling long

Conditions

Castling is allowed only if the following conditions are met:

• Neither the king nor the involved rook has moved yet – so if one of them has moved away, then even if it moves back later, the castling possibility is lost.
• All fields between the king and the involved rook are empty.
• The king is not in check, is not going through check, and it would not arrive into check (this latter follows from the check rule, but the other two do not, so they are extra conditions).

Examples:

White cannot castle, because the king is in check.

White cannot castle, because the king would move through check.

White can only castle to kingside, because on queenside, the king would move into check.

White can castle to queenside, because the king does not move throgh check. (The path of the rook does not matter.)

Notes

Castling is a very strong move as it – uniquely in chess – makes two pieces to move. It moves the king into a safe place, and activates the rook at once.

In chess variants

Though the castling rules can be very different in chess variants, some general rules can be given (but there are exceptions):

• If there is no rook (or similar) or no king, then there is naturally neither castling. For example: Pawn Endgame, Capture all!.
• If the non-pawn pieces do not form a single line as in chess, then generally there is no castling. For example: Balbo's Chess, Gliński's Chess, Circular Chess.
• If the non-pawn pieces form a broken line, then there is castling only on that side which does not have breakpoint. For example: Shifted Chess (V), Four-Bent Chess.
• If the king and the rook are placed similarly as in chess (but probably with different distance), then the castling has similar rules as in chess, but probably the two pieces move different number of fields (the actual number depends on the variant). All fields the king passes must not be attacked. For example: Capablanca's Chess, Los Alamos Chess.

Some examples of different, unusual castling rules:

• Chess 960
• Coregal Chess
• Shafran's Chess

External links

• Wikipedia: Castling