White attacks Black's pawn on e5 with the f-pawn, even though that pawn is itself attacked and undefended. A gambit is an opening that involves a sacrifice of material (chess pieces, usually pawns) for positional gain. In the case of the King's Gambit, White seeks to tempt Black's pawn away from the centre onto f4, which would give White the freedom to play d4 and e5. The move d4 will not only gain centre space but will also uncover an attack by the c1-bishop on Black's f4-pawn, and Black will have to make further non-developing moves to retain the pawn on f4.

Black can accept the gambit with:

• 2...exf4, which is considered the best move, but holding on to the extra pawn is risky. Black must defend very accurately in the resulting sharp positions, or return the pawn later. White cannot yet play 3.d4. This is because the move 2.f4 weakens the e1-h4 diagonal, and 2...exf4 weakens it further by controlling the g3 square. Black can therefore respond with 3...Qh4+!, and since White cannot play 4.g3 due to the Black pawn on f4, White's king is forced out to the second rank in the opening, leaving Black with a better position. Because of this, White usually plays 3.Nf3, preventing Black's queen from occupying h4, or 3.Bc4, allowing White's king to move to f1 instead of e2.

Black may also decline the gambit with one of the following moves:

• 2...Bc5 is the most common way of doing so, taking advantage of the fact that Black's e-pawn cannot be safely captured (3.fxe5?? gets hit by 3...Qh4+! again). Black prevents White from being able to play d4 or to castle kingside without going to some considerable effort to deal with the bishop.
• 2...d5 is the Falkbeer Countergambit, which takes the opportunity to gain space, aiding Black's development.
• 2...Nc6 is known as the Queen's Knight Defense. A possible continuation is 3.Nf3 f5, the Miles Defense.
• 2...d6 is the Nimzowitsch Defense, which often transposes to either the Fischer Defense of the King's Gambit Accepted, or to the 2...Nc6 lines.
• 2...Nf6 is the Petrov Defense, resembling a reversed Latvian Gambit.
• 2...c6, intending ...d5, is possible.
• 2...f5?! is the Panteldakis Countergambit. It is considered dubious with best play, and white gets an advantage, but white must be careful. In the game Kennaugh vs Shirazi, the game continued 3. exf5 e4?! 4. Qh5+ Ke7 5. d3 Nf6! 6. Qg5?!, and black went on to win a wild game^[1].
• 2...Qh4+?! is the Keene Defense. It loses a tempo to 3.g3.
• 2...Qf6?! is playable but does little to help Black.
• 2...c5?! is the Mafia Defense.
• 2...g5? is the Zilbermints Double Countergambit.

Although it was extremely popular in the 19th century, this opening is now very rarely played by professionals due to improvements in technique for Black, though it is still in casual play.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1.e4 e5 2.f4

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Wikipedia has related information at King's Gambit

• Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.