With 2...d6, Black opens the c8-h3 diagonal for his light-squared bishop, and defends the c5-pawn in the future. In addition, Black also controls the e5 square, so Nf6 can be safely played in the future, without any worry of White playing e5.

White has several ways to continue:

White usually continues with 3. d4, the Open Sicilian. With 2. Nf3 inserted, White is able to recapture the pawn after 3...cxd4 with the knight rather than the queen, thus he avoids losing precious tempi with the queen.

White could also play 3. Bb5+, entering the Moscow Variation of the Sicilian, asking Black how he will block the check, and remaining flexible with the d-pawn advance. This also allows White to castle on the next turn.

White could also remain flexible with 3. Nc3, which usually transposes to the Open Sicilian, though by not pushing the d-pawn, White remains flexible on when he wants to open up the position.

White could also play the move 3. Bc4, developing the light squared bishop to an active square putting pressure on f7 and controlling d5, and preparing to castle the next turn, though this is less common, as the bishop is usually a target on c4 to an eventual e6 and d5.

In addition, White can also play a "deferred" Alapin with 3. c3, though with d6 inserted, it usually leads to different positions from the normal Alapin. Black almost always continues with 3...Nf6, taking advantage of the fact that the c3-pawn obstructs the development of the b1 knight, who cannot defend the pawn on e4.

White can also play 3. b4 entering a delayed wing gambit, aiming to play d4 and control the center with 2 pawns, though this is a dubious gambit and very rarely seen today.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 c5 2. Nf3 d6

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Wikipedia has related information at Sicilian Defence

• Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.