The purpose of the present book is to clarify the bridge between Indic exegetical traditions relating to the Ratnagotravibhāga (RGV) and those in Tibet by studying one of the earliest Tibetan commentaries on it, the Theg pa chen po rgyud bla ma’i bstan bcos kyi don bsdus pa by rNgog Blo-ldan-shes-rab (ca. 1059–1109), and in doing so to analyze the historical and doctrinal background bearing on the transmission of the RGV from India to Tibet, and to assess rNgog’s impact upon the later doctrinal development with regard to the RGV. PART I, the historical and doctrinal background, consists of five chapters: Chapters 1 to 5 deal with the authorship of the RGV and the history of its transmission in India up to the 13th century, using Sanskrit, Tibetan, and Chinese materials. Chapter 6 studies six different Tibetan translations of the RGV, and in the process sheds light on how the RGV was transmitted from India to Tibet. PART II, rNgog Blo-ldan-shes-rab and his doctrinal position on Buddha-nature, includes three chapters: Chapter 7 outlines rNgog’s life and writings. Chapters 8 and 9 present rNgog’s philosophical positions, as taught in his RGV commentary. PART III, rNgog’s impact on Tibetan doctrinal developments of Buddha-nature, has two chapters: Chapters 10 and 11 discuss the impact of his interpretations on later Tibetan doctrinal developments. Lastly, final considerations relocate rNgog’s position in a wider context. A critical edition of the first chapter of rNgog’s RGV commentary and an annotated translation of it (both of which were contained in the dissertation thesis of the present author in 2006) will be published as separate volumes, along with critical editions of Sanskrit texts of Sajjana’s Mahāyānottaratantraśāstropadeśa and Vairocanarakṣita’s Mahāyānottaratantraṭippaṇī. Appendix A contains an outline of the entire text of rNgog’s RGV commentary. Appendix B lists all known commentaries on the RGV. For errata to this publication, see a summary of the present book included in Koyasan Daigaku Toshokan Kiyo, vol. 1, 2017, pp. 21–27. For further corrections, see: https://koyasan-u.academia.edu/KazuoKano