Chess Opening Theory/1. e4/1...c5

Sicilian Defence
The moves '''1. e4 c5''' constitute the Sicilian Defence, a counter-attacking opening in which players typically attack on opposite sides of the board. The Sicilian was introduced to the chess world in 1594 by Giulio Cesare Polerio and emerged into the mainstream in the early 20th century as a somewhat tame variation. With the discovery of new attacking ideas, it became Black's most feared weapon by the 1950s and is, pound for pound, the most exhaustively analysed of all openings.

Black's move 1...c5 seeks to create a half-open c-file, controls the important d4 square, and allows the black queen to venture out if desired, while the c-pawn itself is safe from attack, unlike the e-pawn after 1. e4 e5.

White's responses
1...c5 introduces an element of asymmetry into the position; if White were to respond with 2. c4 (the English-like Staunton–Cochrane variation) imitating Black's move, that would weaken the d4 square and make it more difficult to play d4 later on.

Faced with a pawn on c5, White may choose to play 2. d4 (Smith–Morra Gambit) anyway which typically leads to a pawn sacrifice for quick development. After 2...cxd4, White can play 3. c3, sacrificing another pawn in order to play 4. Nxc3 to gain an advance in development in the Morra Gambit.

A more common idea is for White to postpone d4 for a move while they increase their own control of the square. This can be achieved by either 2. Nf3 typically leading to the main lines of the Sicilian (Open Sicilian) or by 2. c3 attempting to establish a strong pawn centre.

Much less common is the attempt to undermine the c-pawn's control of d4 by playing 2. b4 (Wing Gambit) to tempt it off-centre. Since it is considered safe for Black to take the offered pawn and hold on to it, a more recent idea has been to prepare b4 with 2. a3 (Mengarini variation).

White may postpone the fight for d4, typically with 2. Nc3 (Closed Sicilian) though 2. f4 (Grand Prix Attack) is also played. 2. f4 is a violent attacking move, 2. Nc3 typically leads to a more closed and slow-burning position, although f4 frequently appears later.

Statistics
Databases give White approximately 36% winning chances, drawing is at 30%, and Black wins 33%.

Estimated next move popularity: Nf3 74%, Nc3 10%, c3 7%, d4 3%, Bc4 2%, f4 2%, d3 1%, b3 1%, c4 1%, Ne2 1%, g3 0.4%, b4 0.4%, other moves less than 0.3%.

Note that these move frequencies are biased toward databases of stronger players. The next move frequency may be very different for club players. For instance, see the data from the Lichess database below where 2. Nf3 occurs less commonly at only 56% of the time while 2. Bc4 occurs as often as 7% of the time.

Theory table
1. e4 c5