The present edition deals with a tantric image in the historical development of Buddhist theo-philosophy and its impact on Buddhist communities in India and other Buddhist countries. In this edition, I intend to recover the missing links in the history of tantric thoughts through an investigation of the theoretical and practical situations of two important texts which fall between the Tattvasamgraha-tantra and the Hevajra-tantra, that is, the Guhyasamaja-tantra and the Sarvabuddha-samayogadakini-maya samvara-tantra. My investigation is centred upon the practice of svadhidaivatayoga (union with a specific deity of a mandala), which is assumed to be prevalent in the whole course of Tantric Buddhism.