This dissertation is a critical history of Buddhist thought in Japan from 1868 to 1931. During this time, many intellectuals became fascinated with the Buddhism of Japan's medieval period. Some saw it as a form of religious experience that could overcome the modern problem of alienated existence. Others declared that the cultural history of medieval Japanese Buddhism held the essence of Japanese cultural authenticity. These philosophical and historical interpretations of Buddhism together constituted a modern cultural discourse that I call Japanese Medievalism: a romantic vision of medieval Japan as a world of Buddhist spirituality. This dissertation traces the evolution of Japanese Medievalism, reconstructs its main arguments, and examines its ideological significance as a cultural artifact of modern Japan. Japanese Medievalism had an ambiguous ideological function. On the one hand, it was a religious revolt against the ideology of the ruling class - the ideology of the kami (the "native gods" of Japan), which renounced Buddhism as a foreign superstition inimical to national progress. Japanese Medievalism was an attempt to reassert the meaningfulness of Buddhism in defiance of state ideology. But on the other hand, Japanese Medievalism also supported the political order. By evoking a cultural realm of religious experience, Japanese Medievalism diverted attention from the concrete problems of industrial capitalism and anti-democratic politics in Japan. In sum, Japanese Medievalism was a Japanese analog to Existentialism in the West - a spiritual alternative to Marxism's materialist critique of modern society that ultimately had politically conservative consequences.