What is Promotion (chess)?

In chess, promotion is the replacement of a pawn with a new queen, rook, bishop, or knight of the same color. It occurs immediately when the pawn moves to its last rank, with the player choosing the piece of promotion. The new piece does not have to be a previously captured piece. Promotion is mandatory; the pawn cannot remain as a pawn.

Promotion to a queen is known as queening; promotion to any other piece is known as underpromotion. Since the queen is the most powerful piece, promotion is almost always to a queen. Underpromotion may be done for various reasons, such as to avoid stalemate or due to the knight's unique movement pattern. Promotion or the threat of it often decides the result in an endgame.