The Kalacharka Tantra is said to be the most advanced Vajrayana practice there is. It was a text brought into India in the 900s AD and covers as fields of knowledge such as calculations to make calendars, Medicine, and the Kalachakra practice which involves 960 Deities.

This book is a long commentary on this tantra. 

With the encouragement of His Holiness, Geshe Dhargyey graciously consented to give a series of lectures on the subject in the Spring of 1982, while he was in Seattle as a Visiting Professor at the University of Washington. We were fortunate that Venerable Jhampa Kelsang (Alan Wallace) accepted the difficult task of acting as interpreter, and that the ideal environment of the Sakya Tegchen Choling was made available through the kindness of its founders, the Venerable Jigdal Dagchen Sakya Rinpoche and Dagmo Kusho.

The twelve teaching sessions offered between April 3 and June 12, 1982 were transcribed from thirteen ninety-minute tapes.