Chess Opening Theory/1. e4/1...c5/2. Nf3/2...d6

With 2...d6, Black opens the c8-h3 diagonal for his light-squared bishop and defends the c5. ...d6 controls the e5 square, so Black can develop ...Nf6 safely in the future, without any worry of White playing e5. This is the modern, main way for Black to play the Sicilian. The Sicilians with ...d6 include many of the most popular and most theoretical lines in modern chess, including the Najdorf and dragon variations.

3. d4 is the main move. After 3...cxd4 4. Nxd4, White has traded a central pawn for a flank pawn in return for easy development and open lines. The game usually continues 4...Nf6 (attacking d4) 5. Nc3, where Black prevents White from getting in the useful move c3. From there, Black can choose their flavour of ...d6 Sicilian, including the Najdorf (5...a6), classical (5...Nc6), or dragon (5...g6) Sicilians.

The chief sideline to the open Sicilian is 3. Bb5+, the Moscow variation. This develops a piece and prepares to castle. Black must choose how to block the check, usually 3...Bd7, trading off the bishops, or 3...Nd7. White may still open the centre with d4 later.

3. Bc4!?, a delayed Bowdler attack, is playable but less accurate because Black still has the option of ...e6 to relieve the bishop's pressure on f7. On c4

3. Nc3 is flexible and often transposes to the open Sicilian after 3...Nf6 4. d4 cxd4 5. Nxd4, but otherwise White can play in the manner of a closed Sicilian with g3, Bg2 etc.

Rather than blow open the centre, White can play the more conservative [[Chess Opening Theory/1. e4/1...c5/2. Nf3/2...d6/3. c3|3. c3], the "deferred" Alapin, where White may try to support a big, two-pawn centre. With ...d6 inserted however, 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. For now the pawn is defended tactically (4. Be2 Nxe4?? 5. Qa4+ wins the knight), but White must add another defender to e4 before they can play d4.

3. b4?!, a deferred wing gambit, aims to deflect Black's c-pawn from control of d4, so that White may play d4 themselves. After 3...cxb4 4. d4, White has some compensation for lost material the pawn but Black's pawn on b4 can be an annoyance.

1. e4 c5 2. Nf3 d6

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.