Sicilian Invitation

The Sicilian Invitation is the position after 1. Nf3 c5, which Wikibooks also files under the Réti Opening. Black's other main replies, 1...d5 and 1...Nf6, stop White from playing e4. The flank move does not. It stakes out queenside space, watches d4, and offers White an open Sicilian on the next move. The reply suits players who already meet 1. e4 with 1...c5, because White's most direct continuation leads to familiar ground.

The invitation is usually accepted. 2. e4 is the most common reply by a wide margin and reaches the standard Sicilian Defense position after 1. e4 c5 2. Nf3. White players who choose this path give up the flexibility of 1. Nf3 in exchange for the open game. Because the knight is already on f3, lines such as an early f4 or Nc3 setups without Nf3 become less natural.

White has several ways to decline. 2. g3 is the second most frequent reply. It prepares Bg2 and short castling, and White keeps the choice between d3 with e4 and c4 with d4. In online play it scores slightly better than the other main options. 2. c4 moves into the English Opening: Symmetrical Variation, where both sides contest d4 and d5 from the flanks. 2. d4 challenges c5 at once and asks Black to decide how to respond in the center. The engine also rates 2. b3 highly, which heads for a Nimzo-Larsen setup with Bb2 aimed along the long diagonal at the squares ...c5 has left weaker.

The position stays fluid, and many continuations transpose into established openings rather than forming a theory of their own. The choice at move two mostly reflects White's preferences. 2. e4 leads to a heavily analyzed open game, while 2. g3, 2. c4 and 2. b3 give slower maneuvering positions. The engine rates the position as roughly balanced. Results on Lichess are fairly even, with White slightly ahead and few draws.