Kalacakra mandala thangka from the private collection of Sergei Diakoff; photo by Robert Hutwohl. This first truly critical edition of the Sanskrit and two Tibetan translations of the first chapter of the basic text of the Kalacakra tantra provides a definitive text for the study of this important Vajrayana Buddhist scripture. The editor has established the Sanskrit text and presented all the evidence necessary to evaluate every reading. This reveals numerous features of the Sanskrit text that could not be;ascertained in prior editions. In addition, the critical edition of two Tibetan translations for the first time gives us easy access to study the techniques and choices of multiple Tibetan translators, enabling us to fully appreciate their extraordinary skill and their limitations.