Esoteric Tibetan Buddhist scriptures teach practitioners to visualize themselves as deities residing within a mandala. By doing so, they assert, the practitioner will eventually become the deity itself. But are sentient beings instrinsically pure, or does visualization practice make them pure? In this eleventh-century commentary, the renowned Nyingma (Ancient School) scholar Rongzom Chokyi Zangpo sets out his analysis of the nature of purity. This penetrating study, directed towards scholars and serious practitioners, contains Koppl's English-language translation of Rongzom's original text and her explication of his views. Koppl's incisive analysis offers a description of Rongzom's career and works and gives special attention to his critique of Madhyamaka philosophy. Some of Rongzom's approaches, Koppl shows, are unconventional even in a Nyingma context.