Kalachakrayana is a major school in Tantric Buddhism, different from the other major schools of Vajrayana and Sahajayana.
According to Tattva Ratnavali, Mahayana School of Buddhism is sub divided into two schools: Paramitanaya and Mantranaya. The Mantranaya School is the introductory stage of Tantrism in Mahayana Buddhism, and from this other offshoots emerge. Paramita means transcendental, in which Kalachakrayana is said to be the extreme phase of development of tantric Buddhism. In this there is predominance of terrible gods and goddesses who are also named as “demonical Buddhas”.
The word kalachakra means the wheel of time that denotes successive or repetitive progression of beginning and end. Kalachakrayana, vehicle of time, signifies the vehicle which brings the wheel (that causes endless birth and death) under control and offers a safe ride over it to the destination of nirvana.
There is only one text available about this school and it is known as Sri Kalachakra Tantra. The text provides one description of Yoga explained by the omniscient Buddha. Yoga is explained with all its accessories of mandala and consecration within the body. According to it, the universe with all its objects and localities is situated within the body, and time with all its manifestation, such as day, night, fortnight, month, year, etc., exists within the body supported by pranavayu (vital air). The control of vital air is discussed at length in the text, as also the doctrine of kala (time) and the process of keeping oneself above the influence of the spin of time. As Yoa is also an applied discipline, it is an imperative that most of the yogic practices of this school are to be performed in the guru-shishya tradition.