Translated here for the first time into any language, Mountain Doctrine is a seminal fourteenth-century Tibetan text on the nature of reality. The author, Dol-bo-ba Shay-rap-gyel-tsen, was on of the most influential figures of that dynamic period of doctrinal formulation, and his text is a sustained argument about the buddha-nature, also called the matrix-of-one-gone-thus. Dol-bo-ba recognizes two important types of emptiness—self-emptiness and other-emptiness—and shows how other-emptiness is the actual ultimate truth. He justifies this controversial formulation by arguing that it was the favored system of all the early outstanding figures of the Great Vehicle. The translator’s introduction includes a short biography of Dol-bo-ba and an exposition of nine focal topics in his religious philosophy.