The most popular response to 1.e4. Black plays 1...c5, creating an asymmetrical position with winning chances for both sides.
The main line where White plays Nf3 and d4, leading to sharp play.
The Open Sicilian begins after 1.e4 c5 2.Nf3 followed by d4. This is the most principled and popular way to fight the Sicilian.
White plays Nc3 instead of Nf3, leading to more positional play.
The Closed Sicilian avoids the sharp Open Sicilian lines. White builds slowly with a kingside attack.