The first and only commentary on the Buddhist master Longchenpa's essential text on Dzogchen by modern scholar and Nyingma master, Khangsar Khenpo Tenpa'i Wangchuk. Longchen Rabjam (1308-1363), also known as Longchenpa, is a great luminary of Tibetan Buddhism. Regarded as a master of Dzogchen, or Great Perfection, Longchenpa's prolific writings have made him one of Tibet's most renowned and precious teachers. In clear and elegant verse, Longchenpa's Precious Treasury of the Fundamental Nature establishes the definitive view of the ultimate nature of mind according to the secret class of pith instructions of the Great Perfection. Aside from the auto-commentary composed by Longchenpa himself in the fourteenth century, the first and only commentary ever to have been written on this work was composed in the twentieth century by Khangsar Khenpo Tenpa'i Wangchuk, a teacher, scholar, and preserver of Buddhist monastic and scholarly culture in Tibet. This work marks the first step in translating the collected works of this modern Nyingma master. In this commentary, Khangsar Khenpo guides Dzogchen practitioners to experience and understand the phenomena of the outer world detected by the senses as well as the subjective mental and emotional states that apprehend them in order to bring the student to a recognition and stabilized experience of ultimate truth.