The big idea

What the Sicilian Defence is really about.

The most popular and ambitious answer to 1.e4. Instead of mirroring with 1...e5, Black strikes at the centre from the side and refuses a symmetrical game. Black accepts an asymmetrical fight from the very first move and plays for the full point rather than easy equality.

White's plan: Open the centre with an early d4, trade the c-pawn for Black's, and use the space and lead in development to attack — often by castling and storming the kingside while Black is busy on the other wing.
Black's plan: Take on d4 to trade a flank pawn for a central pawn, then develop flexibly and counterattack on the queenside with the half-open c-file, aiming for an unbalanced position with real winning chances.

After 1.e4 c5

A typical Najdorf middlegame: Black has the half-open c-file and a flexible centre, aiming for ...b5 and queenside play (or the ...d5 break) while White attacks on the kingside.

In the Najdorf after ...e5, what is the critical square for both sides?

Answer the question to keep going!