Choosing to promote a passed pawn reaching the 8th rank into a Knight, Rook, or Bishop instead of automatically selecting a Queen.
Why it matters
A queen is the best piece, which is why almost every promotion should be one. Underpromotion is for the two cases where it is not: when a knight comes with check or a fork, and when a queen would stalemate.
It is worth knowing precisely because it is rare — the moment it appears, the player who has never considered it plays the automatic queen and throws the game away.
See it on a board
A new queen does nothing here. A new knight checks the king and hits the queen at the same time.
Checked: this line wins at least 9 pawns of material.
How to play it
- White promotes to a Rook (c8=R!).
- This keeps the game active, provides ample breathing room for the black king, and allows White to execute a clean rook checkmate a few moves later.
At each level
The same idea, said the way it is taught at each age.
Pawn · ages 3–6
When your pawn reaches the end you usually pick a queen. Sometimes a knight is better, because a knight can check in ways a queen cannot.
Knight · ages 4–6
Before you promote, look for a knight check. If the new knight forks the king and something big, take the knight.
Bishop · ages 5–7
The second reason to underpromote is stalemate: if a new queen would leave the enemy king with no moves and no check, take a rook instead.
Rook · ages 6–9
Underpromotion is a calculation habit, not a trick. Add it to the list of candidate moves whenever a pawn touches the seventh rank.
What goes wrong
- Promoting to a queen automatically and giving stalemate.
- Underpromoting for its own sake when a queen wins just as easily — the knight is only better when it does something the queen cannot.
Questions people ask
- When should I promote to a knight?
- When the knight arrives with check or a fork that a queen cannot give, because a queen never moves like a knight.
- Is underpromotion to a rook ever right?
- Yes, to avoid stalemate. A rook can take the same squares as a queen minus the diagonals, which is sometimes exactly enough to leave the enemy king a legal move.