The volumes of the series "Sanskrit Texts from the Tibetan Autonomous Region (SSTAR)" which have appeared until now have made contributions to our knowledge of Indian Buddhism which are of such importance that they may be called revolutionary. The volumes which we are introducing here, however, mark an important new phase in the long-term project of incorporating the treasures preserved in Sanskrit manuscripts in Tibet into the intellectual and spriritual history of mankind. They present, critically edited and translated with annotation, the texts of a scripture, the Buddhakapalatantra, belonging to what was commonly regarded by followers of tantric Buddhism as the highest category of esoteric scriptures, the yoginitantras, and of a commentary thereon by one of the most learned and most influential of Indian Buddhist masters of the early second millenium: Abhayakaragupta.