The Vienna Gambit for White

1.e4 e5 2.Nc3 Nf6 3.f4 d5

The Vienna Gambit is the sharp road of the Vienna Game: after 2.Nc3 Nf6 White pushes 3.f4 against the e-pawn, and the best reply 3...d5 leads to the main line 4.fxe5 Nxe4. White has a pawn on e5 that takes space from Black and a half-open f-file; Black has a strong knight on e4 and free play in the centre. After 5.Nf3 White develops quickly, often with Qe2, and frequently castles long – then the kingside pawns march forward. Stockfish sees the position as almost level, with a small plus for Black in the main line; White is not playing for a refutation here but for a clear, active position with plans of his own. The course rests on 685 games. Black's main roads after 5.Nf3 are 5...Be7 (the Breyer Variation), 5...Nc6, 5...Bg4 (the Kaufmann Variation), 5...Bc5 and 5...Bb4.

The pawn on e5 is the heart of the position: it takes the square f6 from Black's knight and kingside space from Black.
The knight on e4 is Black's best piece – White often trades it with Nxe4 or lets it take on c3 and recaptures with the d-pawn.
After dxc3 White has open lines for the bishop on c1 and the rooks: Bf4, Qe2 and O-O-O are the typical set-up.
With long castling h4 often follows: White advances on the kingside while Black seeks counterplay on the queenside with c5 and the queen on a5.
Against the bishop sorties Bb4 and Bg4 White stays calm: Qe2 guards e5, and Bd2 takes the sting out of the bishop on b4.