King and pawn versus king ending

The king and pawn versus king ending contains exactly three pieces: both kings and one pawn. The pawn side tries to reach the farthest row of the board. On arrival, the pawn must become a queen, rook, bishop, or knight; this change is called promotion. The defender tries to capture the pawn or stop its advance without allowing the opposing king to break through.

Being one pawn ahead does not guarantee a win. The result depends on the locations of both kings, the pawn's square, and whose turn it is. The attacking king usually needs to move in front of the pawn and drive the defender away. The defending king tries to block the route and keep its opponent away from squares from which promotion can be forced.

Ideas that decide the ending

• A key square is a square that lets the attacking king force promotion when it is occupied and play remains accurate.
• Opposition uses the kings' spacing and the move order to make one king yield ground.
• Zugzwang is a position in which being required to move makes the situation worse; it is common when the kings restrict each other.
• Rook pawns, the pawns on the two edge columns, have important exceptions because the attacking king has less room to go around the defender.

This ending is a basic unit of calculation. More complicated endings often simplify into it after the last pieces are exchanged, and a single square or a single turn can change a win into a draw.