The Yoga tantras are the highest of the three groups of so-called “outer” tantras. Compared to the two lower groups, they place more emphasis on the cultivation of internal meditative practices than on external, ritual purity. These internal practices are characterized by the combination of the relative, the method or skillful means (upāya, thabs) of the practice of visualizing oneself as the deity, with the ultimate, the state of non-conceptual wisdom (prajñā, shes rab) inseparable from the deity’s appearances. The principal deity here is Vairocana.
The relatively small number of tantras of this class (fifteen, Toh 479-493) are subdivided into two main groups: those emphasizing method or skillful means, and those emphasizing wisdom.
I. The 8 tantras emphasizing skillful means (thabs gtso bor ston pa’i rgyud):
(a) The root tantra, the Tattvasaṃgraha (Toh 479), the main tantra of this group and an important early tantric work very influential in the development of tantra in China and Japan as well as in Tibet.
(b) Three explanatory tantras (Toh 480-482).
(c) Four supporting (cha mthun) tantras (Toh 483-486). Of these, two (Toh 483 and 484) together represent the eighth century translation of the Sarvadurgatipariśodhana, while Toh 485 is the thirteenth century translation of the same work in the rather different form it had taken in India five centuries later.
II. The 7 tantras emphasizing wisdom (shes rab gtso bor ston pa’i rgyud, Toh 487-493). Among these are duplicates of two of the “tantric” Prajñāpāramitā works (Toh 489 and 491).