King's Gambit, Classical Variation

The Classical Variation of the King's Gambit is a chess opening that begins with the moves:

1. e4 e5

2. f4 exf4

3. Nf3 g5

By playing this move, Black supports the pawn on f4, aiming to prevent it from being recaptured after a later d4 and Bxf4 from White. The move also threatens to kick White's knight on f3 with ...g4, or else to consolidate with ...Bg7 and ...h6. However, the move also weakens Black's kingside. White's most common reply is 4.h4, most often continuing 4...g4 5.Ne5, the Kieseritzky Gambit, the main line of the variation. The next most common is 4.Bc4, most often continuing 4...Bg7, the Traditional Defense, or 4...g4 5.0-0, entering the Muzio Gambit. Also somewhat common are the Rosentreter Gambit, 4.d4, and the Quaade Gambit, 4.Nc3.

3...g5 was the main line of the King's Gambit in the 19th century and remains the most common today, although it is no longer as dominant. After Bobby Fischer lost to Boris Spassky in a 1960 game in the Kieseritzky Gambit, Fischer developed and advocated the alternative 3...d6 in a famous 1961 article in the first issue of the American Chess Quarterly. Both lines are well regarded.

In the Encyclopaedia of Chess Openings, the Classical Variation is given the codes C37 through C39.