This little volume is an attempt at a brief exposition of the philosophical and religious doctrine found in Patanjali's Yoga Sutra as explained by its successive commentaries of Vyasa, Vacaspati, Vijnana Bhikshu and others. The scope of this work is limited to a brief exposition of the intellectual foundation, or the theoretical side, of the Yoga practices, consisting of the philosophical, psychological, cosmological, ethical, religious, and other doctrines which underlie these practices.