Dzogchen, the Great Perfection (Sanskrit atiyoga), is the highest of the nine vehicles in the Nyingma classification of Tibetan Buddhism, and it is also the central teaching of the Bon tradition. Its distinguishing claim is that the nature of mind is already primordially pure and spontaneously perfect, so that realisation is the recognition of what is already the case rather than the construction or attainment of anything new.
The vocabulary follows from that claim. Rigpa is the intrinsic awareness that is recognised. The ground is described as primordially pure (ka dag) and spontaneously present (lhun grub). The practices divide into trekcho, "cutting through" to primordial purity, and togal, "direct crossing", the more esoteric visionary practice undertaken only under close guidance. The relation of teacher to student is structurally central, because the tradition holds that rigpa must be introduced by direct pointing-out instruction and cannot be arrived at by inference.
The tradition traces itself to Garab Dorje and to the eighth-century figures Padmasambhava and Vimalamitra, and a great deal of its literature is transmitted as terma, treasure texts held to have been concealed and later revealed. The Seventeen Tantras and the Nyingthig collections are its principal corpus, and Longchenpa (1308-1364) is its most authoritative systematiser. The nineteenth-century non-sectarian movement in eastern Tibet spread Dzogchen teachings across school boundaries, and both the fifth and the fourteenth Dalai Lamas, though Gelug by institutional affiliation, have practised and taught it.
It has been contested on two fronts. Historically, the antiquity of the Dzogchen tantras was challenged from the eleventh century during the later diffusion of Buddhism in Tibet, by scholars applying strict criteria of demonstrable Indian provenance to texts whose Sanskrit originals could not be produced; the Nyingma defended both the treasure tradition and its own lines of transmission. Doctrinally, critics within Tibetan Buddhism have asked whether a teaching of an already-pure, self-existing awareness can be squared with Madhyamaka emptiness, or whether it reintroduces the very self that Buddhism denies, the same question raised about buddha-nature teaching generally. Dzogchen authors answer that rigpa is empty as well as luminous, is not a substance or an entity, and is not findable when sought.
Modern Western presentations have sometimes detached the practices from the monastic, tantric and preliminary training that the tradition regards as prerequisite. Tibetan teachers have themselves criticised this, and the tradition's own texts warn at length against a conceptual imitation of recognition mistaken for the real thing.