Invented by the Welsh sea captain William Evans in 1827, it was a favourite of 19th-century attackers and regained attention after Kasparov beat Anand with it in the 1990s.
White's plan
The b4 pawn is sacrificed; c3 and d4 build the centre with tempo.
Bishop on c4 and queen on b3 put heavy pressure on f7.
White compensates for the pawn with a lasting initiative and development lead.
Black's plan
Taking the pawn (4...Bxb4) and retreating to a5 is the most common path.
Returning the pawn with ...d6 or ...d5 at the right time to finish development is key.