Vajrayana organizes its tantric literature into graded classes, commonly given in Tibetan systems as action, performance, yoga and highest yoga tantra, each associated with practices of increasing intensity and increasingly strict prerequisites. A practitioner does not simply read a tantric text and begin its practice; access is conferred through an empowerment ceremony, abhisheka, performed by a teacher holding an unbroken lineage of transmission, which is held to ripen the practitioner's capacity to engage the practice safely and effectively. Deity yoga, common across the tantric classes, has the practitioner visualize themselves as an already-awakened being within an ordered environment, a mandala, treating the ordinary sense of a separate, unawakened self as the very obstacle the practice is designed to dissolve, in a method tantric texts describe as swifter than the gradual accumulation of merit over many lifetimes described in sutra-based Mahayana teaching.
The most advanced completion-stage practices of highest yoga tantra, involving subtle-body physiology and, in some lineages, consort practice understood symbolically or, historically and controversially, otherwise, are transmitted only within closed initiatory relationships and are not set out in full even in translated tantric literature available to general readers; scholarly accounts describe their structure and history without reproducing the practices themselves, and this account follows the same limit.