This paper deals with Japanese esoteric Buddhism (Mikkyo), in particular the Shingon tradition, as it relates to the emergence of new and peculiar epistemological concerns. Through a discussion of the kenmitsu system outlined by Kuroda Toshio,the paper first situates Mikkyo within the religious and institutional framework of medieval Japan, underlining its liminal and heterological nature as both an institutionalized discourse and a reservoir of oppositional possibilities. The paper then analyzes the formation of Shingon orthodoxy as an attempt to systematize the Tantric field in Japan through a re-organization of preexisting religious doctrines and practices. Special attention is given to the actual articulation of the kenmitsu episteme and its orders of significance. Finally, the paper outlines some fundamental epistemological tenets of Mikkyo discourse. Though it focuses on Shingon discourse and orthodoxy, this paper confronts basic epistemic assumptions and discursive practices common to the multifarious forms of esoteric Buddhism in Japan.