This work opens up the subject of perhaps the most profound of Buddhist Tantras, The Guhyasamajatantra by shedding light on its relation with previous literature including the Brahmanical tradition and by revealing the elevated type of Yoga. It goes far toward replacing the previous supposition that this Tantra can be understood by mere reading by one oblivious of the extensive commentarial tradition that incorporates the precepts of the Gurus. The author has used the edited Sanskrit texts, the Pradipoddyotana Ms, the relevant texts translated into Tibetan in the Kanjur and Tanjur, and thirteen Tibetan works on the Tantra by Tsong-kha-pa, founder of the Gelugpa sect of Tibetan Buddhism. First he presents the forty Nidana verses that were quoted in Sanskrit in the Pradipoddyotana, and the chapters Six and Twelve of the basic Tantra with some commentarial exposition. Then he initiates the reader into the Tantra by various introductions including a translation of the Guhyasamaja Aksobhya-mandala. There follows a remarkable synthetic commentary on the forty Nidana verses that go with the first 40 syllables of the Tantra. The special teaching of four-stage Yoga is continued into appendices that develop the practical side.