In this book, Annie Besant explains the theory of spiritual development based on the teachings of yoga. In the first lecture, "The Nature of Yoga," Besson speaks on consciousness, what is divine, and how they interrelate. The second lecture regards the six Indian schools of philosophy, mostly comparing and contrasting yoga to Samkhya and Vedanta—the schools that yoga is most closely linked to. The third lecture views yoga as applied science. Finally, the fourth lecture discusses the practice of yoga. The book also contains some discussion of diet and statements on purifying the physical body.