This commentary on Guhyasamaja tantra is the seminal guide to deity yoga and tantric visualization for the Geluk school of Tibetan Buddhism. The Guhyasamaja Tantra, called the king of all tantras, is revered in Tibet, especially by the Geluk school. Ocean of Attainments, a commentary on Guhyasamaja practice, was composed by Khedrup Jé Gelek Palsang (1385-1438), a key disciple of the Geluk school founder, Tsongkhapa Losang Drakpa. It explores the creation stage, a quintessential Buddhist tantric meditation that together with the completion stage comprises the path of unexcelled tantra. In the creation stage, meditators visualize themselves as buddhas at the center of the celestial mandala, surrounded in all directions by male and female buddhas, bodhisattvas, and other enlightened beings. Yet creation-stage practice is not merely visualization but deity yoga--indivisibly uniting the meditation on emptiness with the visualization of the mandala. The creation stage uses the conceptualization in visualization to overcome conceptualization, thereby creating a nonconceptual and nonerroneous direct perception. Such a mind, profound and vast, can bring about a transformation that stops samsaric suffering. How can visions generated as mental constructs not be erroneous? To the awakened eye, the buddhas and other beings who dwell in the mandala are "reality," and in a sense they are more than real. 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 far more detailed, providing extensive scriptural citations, clear explanation of the body maanala, arguments on points of contention, reference to other tantric systems, and critiques of misinterpretations. With its extensive and clear introduction, this volume is a vital contribution to the growing body of scholarship on Guhyasamaja and on Buddhist tantra in general.