The Subject of the present book is that form of Yoga known as Raja Yoga. The Aphorisms of Patanjali are the highest authority and text book on Raja Yoga. The other philosophers though occasionally differing from Patanjali in some philosophical aspect , have as a rule, acceded to his method of practice a decided consent. The first part of this book is comprised of several lecture to classes delivered by the present writer in New York. The second part is a rather free translation of the aphorisms (Sutras) of Patanjali, with a running commentary.