Promotion

A pawn reaching the 8th rank must be exchanged - as part of the same move - for a Queen, Rook, Bishop or Knight of the same colour. The player's choice is not restricted to pieces that have been captured previously. This exchange of a pawn for another piece is called "promotion" and the effect of the new piece is immediate.

The old 19th century rule said that "a pawn could be promoted to any piece except a King", but this sloppy definition left open that pawns could be promoted to pieces of opposite colour (giving your opponent an extra piece).