This commentary on Guhyasamaja tantra is the seminal guide to deity yoga and tantric visualization for the Geluk school of Tibetan Buddhism. Ocean of Attainments was composed by Khedrup Jé Gelek Palsang (1385–1438), one of Tsongkhapa Losang Drakpa’s most prominent disciples. Its subject is the creation stage, a quintessential Buddhist tantric meditation that together with the completion stage comprises the path of unexcelled tantra. The Guhyasamaja Tantra, referred to as the “king of all tantras,” is revered in Tibet, especially by the Geluk school, for its hermeneutic methods, which are in turn applied to other tantras. In the creation stage, meditators visualize themselves as buddhas at the center of the celestial mandala, surrounded in all directions by male and female bodhisattvas and enlightened beings. Since the core of the practice is visualization, this meditation—perhaps more than other meditations—presumes the creative power of the mind. Visualizations form the basis not only of the creation stage and deity yoga but of all tantric practices and rituals, since tantric practice takes place not in mundane existence but in the illusion-like purity of the enlightened view. While the previously published Essence of the Ocean of Attainments is a concise exposition on the practice of the Guhyasamaja sadhana, Ocean of Attainments is much more detailed, providing extensive scriptural citations, clear explanation of the body mandala, arguments on points of contention, reference to other tantric systems, and critiques of misinterpretations. Complemented by the extensive and clear introduction, this volume is a vital contribution to the growing body of scholarship on Guhyasamaja and on Buddhist tantra in general.