Since the late 90's there has been an increase in the number of books available for people wanting information about BDSM and D/s style relationships. I can't say it's a saturated market, but it is overwhelming sometimes trying to find quality material to read that won't leave you confused or stuck in a "this is the only way to do BDSM" sort of mind.
Everyone you ask will give you a different recommended book list - some are great and others are starting to show their age. That's right; some of them feel like they were written ages ago and they probably were. If you want some of the freshest material you want a newer book. At least find one that was written after the advent of the Internet. Trust me, it's worth it.
So, I've taken some of the guesswork out of it for you by providing you the top 3 books I recommend to everyone new to BDSM. The only thing you have to do is figure out which one you want to buy first!
How to be Kinky: A Beginner's Guide to BDSM by Morpheous
This is a fantastically simple book. The information is great for the beginner or nervous and curious bystander. I like the real people images inside - they may be professional but they are definitely of real people and not photoshopped models in latex and rubber. The detail in the information is easy to read, conversational and the tips and quotes in the margins are great! I've gone through this book several times since I reviewed it for Submissive Guide and it doesn't change - it's a solid resource for novices.
The New Topping Book and The New Bottoming Book by Janet Hardy and Dossie Easton
This is actually 2 books, but they cater to whatever side of the slash you reside. So if you are the Top person (Top, Dominant, Master, Daddy/Mommy) you'll want to pick up the Topping book. If you are a bottom (bottom, submissive, slave, pet, baby girl/boy) you'll want the Bottoming book. I love these books because they simply provide those common sense facts that will get you started in BDSM, from identity to safety, community, and play. It's got it all and in bite-sized pieces too.
The Ultimate Guide to Kink: BDSM, Role Play and the Erotic Edge by Tristan Taormino
The Ultimate Guide to Kink is the first major guide to BDSM in a generation—a bold and sexy collection of essays that run the gamut from expert how-to tutorials to provocative essays that delve into complex questions about desire, power, and pleasure. The book brings together diverse voices from the kink community in an unprecedented way: each chapter is written by a different sexuality/BDSM educator.
No matter what book you pick, or all three, I am sure that they will all be a perfect first step for you into BDSM and understand the world you would like to explore.