This dissertation describes the Zur tradition's ( zur lugs ) interpretation of the Mahayoga Vehicle and its central scripture the Secret Essence Tantra ( gsang ba'i snying po rgyud, guhyagarbhatantra ) found in the Old Schools ( rnying ma ) of Tibetan Buddhism. The perspective provided on this tradition is that of an early twentieth century commentary, the Key to the Treasury ( mdzod kyi lde mig ), composed by the Third Dodrupchen Jikme Tenpe Nyima (1865-1926). The first part of the dissertation provides an introduction to the Mahayoga system of beliefs and practices by viewing Mahayoga from four different perspectives: doxographical, historical, scriptural, and philosophical. How Mahayoga figures into the nine vehicle doxography of the Old Schools is presented through a discussion of the relevant section in Oral Instructions of the Lord of Secrets ( gsang bdag zhal lung ) by Lochen Dharmashri (1654-1717), a prominent member of the Zur tradition upon whom Jikme Tenpe Nyima heavily relies. The historical background of the Key to the Treasury is described through short biographies of the important figures in Jikme Tenpe Nyima's lineage along with biographies of other important figures of the Old Schools relevant to this discussion. The scriptural background for the Key to the Treasury is provided through a discussion of the Mahayoga corpus of tantras and means of achievement ( sgrub thabs, sadhana ) along with a chapter summary of the short version of the Secret Essence . Finally, the philosophy of Mahayoga, according to the Zur tradition, is described through summarizing the central points in the first half of the Key to the Treasury . The conclusion of part one provides some tentative hypotheses concerning the origins of the Secret Essence and its Indo-Tibetan lineages along a comparison of the Zur interpretation with the other major hermeneutic tradition, the system of Ronzom Chokyi Zangpo (11 th century) and Longchenpa (1308-1363). Part two of the dissertation contains a translation of the first half of the Key to the Treasury , which describes the general worldview and philosophy of the Zur tradition's interpretation of Mahayoga.
