Evans Gambit for White
1 e4 e5 2 Nf3 Nc6 3 Bc4 Bc5 4 b4
Overview

White's key ideas:

• dominate the center
• get a lead in development
• prevent black from castling (e.g. Bc1-a3)
• get a Q+B battery attacking f7

Black's key ideas:

• get developed
• get castled
• give material back if necessary to do so
• exchange pieces, the bishop with ... Na5

Black must decide whether to capture zero, one, or both of White's pawns on d4 and c3.

If white gets the ideal center, then he generally has sufficient compensation for the pawn.

When Black gets greedy and grabs both pawns, White get ample compensation - a strong attack.

According to theory, Black should not take either. He should develop quickly, often including Bb6 and Na5.