Yantra Yoga, the Buddhist parallel to the Hathayoga of the Hindu tradition, is a system of practice entailing bodily movements, breathing exercises, and visualizations. Originally transmitted by the mahasiddhas of India and Oddiyana, its practice is nowadays found in all schools of Tibetan Buddhism in relation to the Anuttaratantras, more generally known under the Tibetan term trulkhor, whose Sanskrit equivalent is yantra. The Union of the Sun and Moon Yantra (Phrul 'khor nyi zla kha sbyor), orally transmitted in Tibet in the eighth century by the great master Padmasambhava to the Tibetan translator and Dzogchen master Vairochana, can be considered the most ancient of all the systems of Yantra, and its peculiarity is that it contains also numerous positions which are also found in the classic Yoga tradition. Chögyal Namkhai Norbu, one of the great living masters of Dzogchen and Tantra, started transmitting this profound Yoga in the seventies and at that time wrote this commentary, which is based on the oral explanations of some Tibetan yogins and siddhas of the twentieth century. All Western practitioners will benefit from the extraordinary instructions contained in this volume.