Namkhai Nyingpo
Mahayoga (rnal 'byor chen po).
The first of the 'Three Inner Tantras.' Mahayoga as scripture is divided into two parts: Tantra Section and Sadhana Section. The Tantra Section consists of the Eighteen Mahayoga Tantras while the Sadhana Section is comprised of the Eight Sadhana Teachings.
Jamgön Kongtrül says in his Treasury of Knowledge: "Mahayoga emphasizes means (upaya), the development stage, and the view that liberation is attained through growing accustomed to the insight into the nature of the indivisibility of the superior two truths."
The superior two truths in Mahayoga are purity and equality — the pure natures of the aggregates, elements and factors of the senses are the male and female buddhas and bodhisattvas. At the same time, everything which appears and exists is of the equal nature of emptiness. [RY]