Bernie Clark is the big name in Yin yoga, which is my favorite type of yoga, as I get older. In addition to giving a good dictionary of poses and some sequences, this book offers a lot of knowledge and food for thought, about the how and why of Yin yoga. His ultimate goal is to prove, from both the Eastern perspective (the panchamayakosha system, the Chinese meridian system) and the Western perspective (anatomy, science), that Yin is doing real work in terms of healing and strengthening the body and mind.
Sometimes it feels he's just woolgathering, and he definitely only scratches the surface on the meridians, but this is basically a master class in the subject. An absolute MUST for yoga instructors and for people who want something a little deeper than, say, the Yin yoga resources from Yoga Journal, etc. Not to take away from those books! Those are great! This is just...greater if that's what you're looking for.