The Sicilian Najdorf

https://www.chess.com/forum/view/chess-openings/is-the-sicilian-meant-for-chess-experts-only

"Generally speaking, 'Starting Out' and 'Sicilian Najdorf' are not exactly words that one envisions in the same title, because anyone who is just starting out should not dive into the vast ocean of theory that is the Najdorf. For beginners, the time invested in studying even minor lines can be more productively used solving tactical puzzles and basic endgame technique.
...
... In some lines, a good understanding of basic principles will take you far, while in others, such as the Poisoned Pawn (6 Bg5 e6 7 f4 Qb6!?), memorization is a must, as one wrong move can cost you the game in the blink of an eye. ...

... It is a pleasure to recommend this book to those who want to get further acquainted with this opening." - FM Carsten Hansen (2006)
https://web.archive.org/web/20140626175558/http://www.chesscafe.com/text/hansen87.pdf

I liked "Play the Najdorf Sicilian" by James Rizzitano. It was fairly straightforward and gave you all the major lines. I'm just beginning to figure it out after playing a lot of games with the Najdorf (I'm up a piece in a game right now). I switched from the Dragon and then the Taimanov Sicilian.