Mahāmudrā, “the Great Seal,” is a Sanskrit term (Tibetan: phyag rgya chen po) that connotes a wide range of concepts and practices in Indian Mahāyāna and, especially, Tibetan Buddhism, most of them directly or indirectly related to discourse on ultimate reality and the way to know and achieve it. The term first appeared in Indian tantric texts of the 7th or 8th century ce and gained increasing prominence in the final period of Buddhism’s efflorescence on the subcontinent, particularly in the sometimes transgressive Mahāyoga and Yoginī tantras and the works of such charismatic great adepts (mahāsiddhas) as Saraha, Tilopa, and Maitrīpa. By the 11th century, Mahāmudrā had come to refer, in India, to a hand gesture signifying clear visualization of a deity, one of a number of “seals” (with or without hand gestures) that confirm tantric ritual procedures, a consort employed in sexual yoga practices, a meditation technique in which the mind contemplates its own nature, the great bliss and luminous gnosis that result from advanced subtle-body practices, a way of living in the world freely and spontaneously, and the omniscient buddhahood that is the final outcome of the tantric path. It also came to be synonymous with such concepts as emptiness, the middle way, sameness, the co-emergent, the natural mind, luminosity, the single taste, non-duality, meditative “inattention,” buddha nature, non-abiding nirvāṇa, and a buddha’s Dharma Body—to name just a few. Although little discussed during the period of Buddhism’s introduction to Tibet (c. 650–850), Mahāmudrā came to the fore on the plateau during the so-called Tibetan Renaissance (c. 950–1350), finding a place of greater or lesser prominence in the ideas and practices of the religious orders that formed at that time, including the Kadam, Sakya, Shijé, Shangpa Kagyü, and—most notably—the powerful and influential Marpa Kagyü, for which it is a pivotal term, referring to the true nature of the mind, a style of meditation aimed at the realization of that nature, and the perfect buddhahood resulting from that realization. Although it has all these meanings and more, Mahāmudrā became best known as a contemplative technique in which the mind realizes, and settles within, its own true nature: as empty and luminous. It was brought to the center of Kagyü religious life by Gampopa (1079–1153), and studied, practiced, and systematized by generations of great Kagyü scholars and meditators. In later times, it sometimes inspired syncretic formulations, which combined the practices of Kagyü Mahāmudrā with those of the Nyingma Great Perfection (Dzokchen), or the Gelukpa analysis of the emptiness of all existents. Over the course of a millennium or more in Tibet, the Great Seal informed ritual, prompted ecstatic poetry, provoked debate, became the focus of yogic retreats, and was used as a lens through which Indian Buddhist thought and Tibetan institutional history might be viewed. With the post-1959 Tibetan disapora and the subsequent spread of Tibetan Buddhism outside Asia, Mahāmudrā has become a topic of interest for scholars and practitioners in many and varied settings, and a part of the vocabulary of educated Buddhists everywhere.