One of the highest class of Buddhist Tantra-s were known as Anuttarayoga Tantra (Tibetan: bla na med pa’i rgy) meaning Unexcelled Tantra. In the new schools of Tibetan Buddhism it is associated with the mahamudra route to enlightenment. In the Gelug tradition it is believed this Tantras originated from the teachings of the Buddha on how to transform sense pleasures into a quick path of enlightenment, and this in turn depended on the ability of the sadhaka to dissolve the prana into the central channel of awareness by force of concentrated meditation.
In the classification of the Dzogchen system, used by the Nyingma, anuttarayoga is equivalent to the Mahayoga tradition by which the seeker eventually reaches Buddhahood. This yoga is to be practiced only under instructions of a qualified Lama, and involves a plethora of techniques by which eventually the seeker unites his mindstream with that of the deity he is worshiping.
Five collections of Anuttarayoga tantras became prominent in Tibet initially: Guhyasamāja or ‘Esoteric Community’, Yamāntaka or ‘Death Conqueror’ (alternatively known as Vajrabhairava or ‘Vajra Terrifier’), Hevajra or ‘O, Vajra!’, Mahāmāyā or ‘Great Play of Illusion’ and Cakrasaṃvara or ‘Wheel of Great Bliss’. The Kālacakra or ‘Wheel of Time’ tantra, came about later. These were further subdivided into two major classes: Father Tantras and Mother Tantras and non-dual Tantras.
The practices which were popular during the reign of the Pala Empire in Eastern India, became known in Tibet as the Father Tantras or pha rgyud. They emphasized the use of anger as a method realizing the emptiness of Buddha nature. Whereas the yoginī-tantras became known in Tibet as ‘Mother Tantras’ (ma rgyud) emphasized the development of enlightened awareness or the mind of clear light or prabhāsvara, transforming desire (tṛṣṇā) through devotion. The most famous Tantra in this category was the Cakrasaṃvara, from which the practice of Vajrayogini evolved later on.
The 3rd category of Tantras were called non-dual which utilize both anger and desire as an antidote to delusion (avidyā). The most famous of this class of Tantras is the Kalachakra Tantra.