In the history of Buddhist scholarship it has been the convention to treat the Madhyamaka and Yogacarin strands of the Mahayana as separate and fundamentally opposed schools of thought. This thesis represents an attempt to explore the relationship between the two in some detail and comes to the conclusion that earlier assessments are not justified by either textual evidence, or by underlying trends in the history of the development of Buddhist thought as such. The overall substance of the thesis is a general reappraisal of the ontological and epistemological doctrines contained in the writings of Nagarjuna, Asanga and Vasubandhu with particular reference to the earliest Buddhist philosophical texts available. By turning to the texts themselves, and assigning a lesser significance to the commentarial literature of a later period, it is possible to show considerable overlap in all areas of doctrine, but particularly the treatment of the levels of truth, the understanding of the enlightened and the unenlightened states and their relation to an indeterminate existence realm, the nature of that real, and finally the function and status of language and thought. As a result of these investigations it is possible to erect a new theory to explain the proliferation of Indian Mahayana Buddhism which does not operate on a schismatic basis, but rather accounts for variety as the consequence of individual authors addressing new audiences, and specific contemporary problems, from a firm and consistent doctrinal bedrock.