1 e4 c5 2 Nf3
(1 Nf3 c5 2 e4)

2...d6 2...e6 2...Nc6 2...a6 2...Nf6

The Ideas Behind the Chess Openings; Fine, Reuben (rep.1990). Some of the lines may be dated, but virtually none of the concepts are, and Fine is one of the best teachers. --Macheide