Castling

Castling

Castling is a special chess move where the king moves two squares toward a rook, and the rook jumps to the square the king crossed over, all in a single turn. It's the only move where you can move two pieces at once, and it serves to both protect the king and bring the rook into play. To castle, the king and the rook cannot have moved previously, the path between them must be clear, and the king cannot be in or pass through check.

How to castle 

King-side: The king moves two squares toward the kingside rook, and the rook moves to the square just inside the king. This is notated as  0-0

Queen-side: The king moves two squares toward the queenside rook, and the rook moves to the square just inside the king. This is notated as  0-0-0