Evans Gambit
Italian Game
1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.b4 Bxb4 5.c3 Ba5 6.d4 d6 7.Qb3 Qd7
White sacrifices the b-pawn to gain rapid development and a strong center.
Fun fact: Captain Evans first tried his gambit against Alexander McDonnell in London, in a game usually dated to 1827. Source
Practice this lineThe idea
White gives up a pawn with 4.b4 to deflect Black's bishop and gain time. After 4...Bxb4 5.c3 the bishop is attacked again, and White is ready to play d4 with a big center and quick development.
This line continues 5...Ba5 6.d4 d6 7.Qb3 Qd7. White's queen joins the bishop on c4 in pressing f7, and Black's queen on d7 guards that square along the seventh rank.
Plans for White
Use the lead in development before Black untangles. The usual continuations from here are 8.dxe5 and 8.O-O, bringing more pieces into play and opening lines toward Black's king.
Don't rush to win the pawn back. The time and open lines are White's compensation, and they matter more than material while Black is still undeveloped.
Plans for Black
Black keeps the extra pawn for now, but the real goal is to finish development and get the king to safety. Be ready to give the pawn back when that frees the position.
Modern analysis says Black can defend and reach roughly equal positions, but over the board the defender has the harder job.
Watch out for
Black's biggest danger is grabbing too much. If Black takes on d4 instead of playing 6...d6 here (6...exd4 7.O-O dxc3?!, the "Compromised Defense"), White answers 8.Qb3, lining up on f7 again. With e5 and Nxc3 to follow, White gets a very dangerous attack for the two pawns.
White's danger is running out of steam. If the attack stalls and Black gets castled with the extra pawn, the endgame favors Black. Keep bringing pieces in before Black consolidates.
The Compromised Defense
6...exd4 7.O-O dxc3 8.Qb3 Qf6 9.e5 Qg6 10.Nxc3 Nge7 11.Ba3
History
The gambit is named after Captain William Davies Evans, a Welsh sea captain. It was one of the most popular openings of the 19th century, then went out of fashion once good defenses were worked out. One of them is Lasker's Defense, 6...d6 7.O-O Bb6, in which Black gives the pawn back to reach a quiet, queenless endgame.
Garry Kasparov revived the gambit at the top level in 1995, most famously with a 25-move win against Viswanathan Anand in Riga.