I started in Iyengar yoga, and so this is practically the bible for me of poses, alternatives when I can't complete the pose, etc. However, even if you do other styles of yoga this book will be very useful for identifying proper posture in each pose that each yoga type uses. It's also good for indicating certain poses that are recommended or discouraged given health conditions.
Very clear instruction, pictures and well-organized! A must have!!

This is the best yoga book because it gives excellent guidance to perform the postures safely which is very important. I'm doing specific postures for a health issue and they really work. I am amazed by the power in them to affect healthy functioning of the body. I highly recommend it along with diet and other approaches to resolving health issues.