Sicilian Defence

The Sicilian Defence is a chess opening which begins with::1.e4 c5This is the most popular response at master level to 1.e4. Black immediately fights for the centre, but by attacking from the c-file (instead of mirroring White's move) he creates an asymmetrical position that leads to complicated situations. Typically, White has the initiative on the kingside while Black obtains counterplay on the queenside, particularly on the c-file after the exchange of Black's c-pawn for White's d-pawn.

The opening was named by Gioacchino Greco in the 17th century.

Open Sicilian

The common Sicilian variations start with the moves 1.e4 c5 2.Nf3, when there are three main continuations for Black: 2...d6, 2...Nc6, and 2...e6. White then plays 3.d4, when black replies with 3...cxd4. The resulting position is one of the most complex in modern chess practice, as white's advantage in development and space is counterbalanced by black's central pawn majority and open c file.

2...d6

The most common move, Black's move opens up for his bishop and defends the e5 square. Play usually continues 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 when Black usually winds up playing the Dragon (5...g6), Najdorf (5...a6), Classical (5...Nc6), or Scheveningen (5...e6).

Dragon

Black can adopt a variety of set-ups, among them the Dragon variation, which begins

1.e4 c5:2.Nf3 d6:3.d4 cxd4:4.Nxd4 Nf6 :5.Nc3 g6

In this variation, Black fianchettoes a Bishop on the h8-a1 diagonal. This is called the "Dragon" variation, by one account because Black's kingside pawn structure looks like the constellation "Draco". It is also suggested that the name is a reference to the pawn structure's resemblance to dragon scales. Or in a more chess minded manner of thinking, the fianchettoed bishop on g7 is then able to "breathe fire" down the diagonal. Another possible reason for the name is that a very aggressive middlegame usually develops following opposite-side castling. The dragon has a reputation for being a very aggressive opening.

Najdorf

The most popular Sicilian system is the Najdorf, which begins

1.e4 c5:2.Nf3 d6:3.d4 cxd4:4.Nxd4 Nf6:5.Nc3 a6

White plays a variety of moves here, including 6.Bg5, 6.Be2, 6.Be3, Bobby Fischer's preferred response 6.Bc4, 6.f3, 6.f4, 6.g3, and, rarely, 6.h3 or even 6.Rg1 (Jovan Petronic), preparing 7.g4.

Classical

After:1.e4 c5:2.Nf3 d6 :3.d4 cxd4:4.Nxd4 Nf6:5.Nc3 Nc6, the so-called "Classical" Sicilian arises, featuring sound natural development from both sides. Both sides have brought out their knights to the best squares. White usually continues with 6.Bg5 (the Richter-Rauzer Variation), which aims to weaken the Black kingside with a timely Bxf6 when Black often must respond with the weakening ...gxf6. In return, Black will enjoy a useful majority of pawns in the centre. Another popular variation is 6.Bc4, the Sozin Variation, which brings the bishop to an aggressive square, and allows white to castle on either the kingside or the queenside (the hyper-aggressive Velimorovic Attack). The Sozin Variation was a favorite of Bobby Fischer. Less popular moves are 6.Be2, 6.Be3, 6.f3, 6.g3, and 6.f4.

Scheveningen

:1.e4 c5:2.Nf3 d6 :3.d4 cxd4:4.Nxd4 Nf6:5.Nc3 e6 The Scheveningen gives Black a small defensive centre, but which can be useful in preventing a White assault there while Black concentrates on the queenside. A surprising but dangerous attempt for White is the Keres Attack, beginning with 6. g4.

Moscow

:1.e4 c5:2.Nf3 d6 :3.Bb5+This is a simplifying line, also known as the Canal-Sokolsky variation, is a fairly popular alternative if White wants to avoid the mainline theory. This variation was played by Garry Kasparov in the online game Kasparov versus The World.

Other

White can also keep his options open with the "Chameleon System" championed by Soltis and others, a typical line of which runs 2. Nc3 d6 3. Nge2, keeping Black guessing whether White will play a Closed Sicilian with 4.g3 or transpose to a standard Open Sicilian with 4. d4.

2...Nc6

By playing 2...Nc6 Black develops the knight to a natural square. Play often transposes to the Classical variation given under 2...d6, but there are some major alternatives.

Sveshnikov

:1.e4 c5:2.Nf3 Nc6:3.d4 cxd4:4.Nxd4 Nf6:5.Nc3 e5That's the start of the Sveshnikov variation, also called Lasker-Pelikan in some texts, whose recognised main-line goes as follows::6.Ndb5 d6:7.Bg5 a6:8.Na3 b5 (the old Bird sub-variation 8...Be6 is playable but less rated nowadays):9.Bxf6 (the positional 9.Nd5 is a valid and popular alternative) gxf6:10.Nd5This variation (pioneered by Evgeny Sveshnikov) has become very popular in master level chess. Black's play seems anti-positional, making the d6 pawn backward and potentially weak, creating a hole in Black's position on the d5 square, and allowing White to break up Black's kingside pawn structure. In fact 9...Qxf6?! 10.Nd5 Qd8 gives White more than its typical opening advantage by means of 11.c4 (11...b4? 12.Qa4 Bd7 13.Nb5! axb5 14.Qxa8 Qxa8 15.Nc7+ is a well known trap) or even 11.Bxb5!? axb5 12.Nxb5 Be7 (12...Qa5+ 13.c3!; 12...Ra5?? 13.Nbc7+ Kd7 14.Qg4+ f5 15.Qxf5 mate) 13.Nbc7+ Kf8 14.Nxa8 Qa5+ 15.c3 Qxa8.

However, there are a number of compensating factors for Black in the position. Black gets a foothold in the centre, a strong mass of central pawns with the ability to play ...f5 without opening the e8-h5 diagonal, and good piece activity, whereas White is forced to move his knight several times only for it to end up out of play on a3. Black also enjoys the advantage of the bishop pair (after 9.Bxf6), although in some lines Black is willing to exchange back the dark-squared bishop for a knight since such bishop can't contribute to the fight for the d5 square.

Accelerated Dragon

:1.e4 c5:2.Nf3 Nc6:3.d4 cxd4:4.Nxd4 g6The Accelerated Dragon features an early ...g6 from Black. An important difference between this line and the Dragon is that Black avoids playing ...d7-d6, so that he can later play ...d7-d5 in one move if possible. Black also avoids the Yugoslav attack, but since White has not been forced to play Nc3 yet, the option of playing c4 (the Maróczy bind) becomes available. Generally, this opening features a more positional style of play, unlike many of the other sicilian variations.

Rossolimo

:1.e4 c5:2.Nf3 Nc6:3.Bb5Like the Moscow variation, White plays an early Bb5, usually with the intention of trading it for the c6-knight and giving Black doubled pawns. Blacks most usual continuation is to quickly developed by 3...g6, although moves like 3...Qc7, 3...Qb6 and 3...e6 are also possible.

Other variations

Sometimes Black plays such moves as an early ...Qb6 which brings more attackers against the d4 square (e.g. 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Qb6, known as the Grivas Sicilian).

2...e6

This is a flexible, although less aggressive alternative. Transpositions to the Scheveningen are quite common, but there are some other variations which are also popular.

Taimanov

:1.e4 c5:2.Nf3 e6:3.d4 cxd4:4.Nxd4 Nc6The Taimanov is named after Mark Taimanov. Black develops the knight to a natural square and keeps options open for where to put the other pieces. One of the ideas of this system is to develop the King's Bishop to b4 or c5. White can prevent this by 5.Nb5 d6 6.c4, establishing a Maróczy bind.

Kan

:1.e4 c5:2.Nf3 e6:3.d4 cxd4:4.Nxd4 a6By playing 4...a6, Black prevents the White knight from jumping to b5, as well as preparing an eventual ...b5 advance. The main purpose of this variation is to retain maximum flexibility. Black waits for White to move before choosing a plan. White's most popular replies are 5.Nc3, 5.Bd3, and 5.c4.

Other moves in the Open Sicilian

After 1.e4 c5 2.Nf3, Black has some other options including:
*2...Nf6 is the Nimzowitsch variation which allows White to chase the knight by 3.e5. It bears some similarity with the Alekhine Defense.
*2...g6 is the Hyper-Accelerated Dragon, bearing strong resemblance to the "normal" Accelerated Dragon.
*2...a6 is the O'Kelly Variation.

Other systems

To avoid giving Black this wide choice of systems, White can adopt a number of so-called "anti-Sicilian" lines, including:
*2.Nc3 followed by g3 (the Closed Sicilian).
*2.Nc3 followed by f4 (the Grand Prix Attack), a typical line of which runs 2.Nc3 Nc6 3.f4 g6 4. Nf3 Bg7 5. Bc4 e6 6.f5.
*2.Na3 A rare continuation recently dug up by Vadim Zvjaginsev against his game with Alexander Khalifman in the 58th Russian Championship Superfinal, that brought him victory.
*2. c3 (Sicilian Defense, Alapin Variation.
*2. d4 cxd4 3. c3 (the Smith-Morra Gambit).
*2. b4?! (the Wing Gambit).
*2. g3 (which may transpose to the Closed Sicilian but offers other options -- such as 2...d5 for Black, and a centre buildup with c3 and d4 for White).
*2. c4.
*2. b3.
*2. f4 (named "McDonnell Attack" from McDonnell - De La Bourdonnais London 14th game 1834) An ambitious attempt to achieve a more flexible Grand Prix setup by White is 2. f4. This has the disadvantage of allowing 2...d5 (the Tal Gambit) which is playable as a pawn sacrifice (3.exd5 Nf6). However, White may refuse this with the Tal Gambit Declined via 3. e5 or 3. Bb5+ or 3. Nc3, leading to the so-called Toilet Variation, named after the inventor's original place of inspiration.

ECO codes

The Encyclopaedia of Chess Openings has given all the codes from B20 to B99 to the Sicilian, giving this opening more codes than any other opening. In general these guidelines apply:
*The B20 series (B20-B29) covers the sidelines where White does not play 2.Nf3. The codes B27 to B29 however cover 2.Nf3 variations, B27 has rare second move responses from Black, B28 covers the O'Kelly Variation (2...a6) while B29 covers the Nimzovitsch Variation (2...Nf6).
*The B30 series covers the lines beginning 1.e4 c5 2.Nf3 Nc6 and which do not have an early ...d6 (which would usually put the opening into the B60 series). The most important variations here are the Rossolimo, Kalashnikov, Sveshnikov and Accelerated Dragon.
*The B40 series covers the lines beginning 1.e4 c5 2.Nf3 e6, most importantly the Taimanov and Kan variations.
*The B50 series covers the sidelines of 1.e4 c5 2.Nf3 d6. Here is the Moscow Variation (3.Bb5+), Chekhover Variation (3.d4 cxd4 4.Qxd4) and some other rare lines such as 3.d4 cxd4 4.Nxd4 Nf6 5.f3. The codes B56 to B59 also cover some lines of the Classical, most importantly the Sozin Variation.
*The B60 series covers the Richter-Rauzer Variation of the Classical Sicilian.
*The B70 series covers the normal (unaccelerated) Dragon Variation.
*The B80 series covers the Scheveningen Variation.
*The B90 series covers the Najdorf Variation.