Maitreya’s Distinction between Phenomena and the Nature of Phenomena distinguishes the illusory phenomenal world of saṃsāra produced by the confused dualistic mind from the ultimate reality that is mind’s true nature. The transition from the one to the other is the process of “mining for wisdom within delusion.” Maitreya’s text calls this “the fundamental change,” which refers to the vanishing of delusive appearances through practicing the path, thus revealing the underlying changeless nature of these appearances. In this context, the main part of the text consists of the most detailed explanation of nonconceptual wisdom—the primary driving force of the path as well as its ultimate result—in Buddhist literature. The introduction of the book discusses these two topics (fundamental change and nonconceptual wisdom) at length and shows how they are treated in a number of other Buddhist scriptures. The three translated commentaries, by Vasubandhu, the Third Karmapa, Rangjung Dorje, and Gö Lotsāwa, as well as excerpts from all other available commentaries on Maitreya’s text, put it in the larger context of the Indian Yogācāra School and further clarify its main themes. They also show how this text is not a mere scholarly document, but an essential foundation for practicing both the sūtrayāna and the vajrayāna and thus making what it describes a living experience. The book also discusses the remaining four of the five works of Maitreya, their transmission from India to Tibet, and various views about them in the Tibetan tradition.