Here are several books we love and recommend. Follow the links below to buy them on Amazon.
Light on Yoga: The Bible of Modern Yoga
The Key Muscles of Yoga: Scientific Keys, Volume I
Teaching Yoga: Exploring the Teacher-Student Relationship
Turning the Mind Into an Ally
Yoga Sutra Translations:
Inside the Yoga Sutras: A Comprehensive Sourcebook for the Study & Practice of Patanjali's Yoga Sutras
The Yoga Sutras of Patanjali