This volume is the last book in the six-volume edition of Letters on Yoga in Russian. This book discusses the transformation of a person’s physical being, which should become the culmination of his internal, spiritual transformation and lead to the appearance on Earth of a new, “superhuman” being, possessing not only a divine, “supramental” consciousness, but also an immortal body. Such a radical and comprehensive transformation is fraught with numerous difficulties and dangers caused by the confrontation between the hostile forces of the subtle-material planes of existence. Therefore, this book is extremely important for those who intend to practice Integral Yoga, as it contains detailed explanations and recommendations designed to make spiritual practice safe.