The texts in this subsection are works on tantras classified as belonging to the highest of the four classes of tantra according to the gsar ma (“new”) traditions. The Tibetan term for the Unexcelled Yoga class, rnal ’byor bla na med pa’i rgyud, has traditionally been back-translated into Sanskrit as anuttarayogatantra, but this term is not attested in Sanskrit texts; using forms that are attested, yoganiruttaratantra or yogottaratantra are preferable.
The Unexcelled Yoga tantras are characterized by the practices of the two phases of generation and completion, by their approach to the deity as inseparable in all respects from the practitioner, and by their emphasis on wisdom or awareness (jñāna, ye shes).
Tantras of this class are subdivided into three main groups: non-dual tantras (gnyis med kyi rgyud), mother tantras (ma’i rgyud), and father tantras (pha’i rgyud). The mother tantras emphasize wisdom (prajñā, shes rab), while the father tantras emphasize method or skillful means (upāya, thabs), and a third category, non-dual tantras—placed above the other two—emphasize the union of wisdom and means.
The elements taught in different tantras, and statements made in them, have been used by Tibetan scholars in a variety of ways to classify them into these three groups, which were probably never explicitly recognized or defined in India. Nor, indeed, did Tibetan scholars always agree on the categories concerned, as can be seen from the differences even between the Kangyur and Tengyur in the way individual tantra cycles are placed by their editors in their respective catalogues (dkar chag).
For further details on the Tibetan tradition’s classification of tantras, see:
Jamgön Kongtrul (’jam mgon kong sprul blo gros mtha’ yas), shes bya kun khyab, Delhi: Shechen Publications (1997), section 6, chapter 4. Translated as Guarisco, E. and McLeod, I (trans.), The Treasury of Knowledge: Book 6, Part 4, Systems of Buddhist Tantra, Ithaca: Snow Lion Publications (2005), especially chapters 2 and 15.
Tsongkhapa, A Lamp to Illuminate the Five Stages, tr. Kilty, Gavin. Library of Tibetan Classics; Boston: Wisdom Publications (2013). Chapter Two, “The Two Types of Tantra,” discusses different views on the division of tantras into “mother” (wisdom) and “father” (method) types.