The Rousseau Gambit is a chess opening

Chess opening

A chess opening is the group of initial moves of a chess game. Recognized sequences of opening moves are referred to as openings as initiated by White or defenses, as created in reply by Black. There are many dozens of different openings, and hundreds of named variants. The Oxford Companion to...

 characterised by the moves:

1. e4 e5

2. Nf3 Nc6

3. Bc4 f5

The gambit is named after Eugène Rousseau

Eugéne Rousseau (chess player)

Eugène Rousseau was a French chess master. He was the strongest chess player in New Orleans in the first half of the 1840s. The Rousseau Gambit is named after him....

. White's best response is to decline the gambit by supporting the e pawn

Pawn (chess)

The pawn is the most numerous and weakest piece in the game of chess, historically representing infantry, or more particularly armed peasants or pikemen. Each player begins the game with eight pawns, one on each square of the rank immediately in front of the other pieces...

 with 4. d3. The resulting position is similar to a King's Gambit

King's Gambit

The King's Gambit is a chess opening that begins with the moves:White offers a pawn to divert the Black e-pawn so as to build a strong centre with d2–d4...

 Declined with colours reversed, and White's king bishop

Bishop (chess)

A bishop is a piece in the board game of chess. Each player begins the game with two bishops. One starts between the king's knight and the king, the other between the queen's knight and the queen...

 aiming at Black's weakened kingside. Black will have trouble castling

Castling

Castling is a special move in the game of chess involving the king and either of the original rooks of the same color. It is the only move in chess in which a player moves two pieces at the same time. Castling consists of moving the king two squares towards a rook on the player's first rank, then...

 kingside and Ng5 is a likely threat. White's position is better, but still requires careful play.

Key themes for White are to attack Black's kingside and to avoid attempts by Black to simplify the position. Exchanges involving White's light bishop are particularly suspect.

The best advice for Black is to not play this gambit as it is considered refuted.

Rousseau Gambit Declined

White's best response is to decline the gambit and to wait to capture the f pawn.

1. e4 e5

2. Nf3 Nc6

3. Bc4 f5

4. d3

Rousseau Gambit Accepted

White still has a good game after the inferior 4.exf5, but the position is less clear. Black usually plays 4...e4, which White may meet by 5.Nd4! Nf6 (5...Nxd4? leads to trouble after 6.Qh5+) 6.Nxc6.

1. e4 e5

2. Nf3 Nc6

3. Bc4 f5

4. exf5

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