The Rousseau Gambit (or Ponziani Countergambit after Domenico Lorenzo Ponziani) is a chess opening that begins with the moves: The gambit is named after French chess master Eugène Rousseau.

The resulting position is similar to a King's Gambit Declined with colours reversed, and White's king bishop aiming at Black's weakened kingside.

Exchanges involving White's light-square bishop are particularly suspect.

White can decline the gambit and wait to capture the f-pawn.

White still has a good game after the inferior 4.exf5, but the position is less clear.