The present work raises many challenging questions in regard to the nature and functional role of Buddhism in the history of Indian ideas.Beginning with a general survey of the history of researches on Buddhism, it makes a reassessment of the views on the origins of Buddhism put forward by eminent scholars and deals with the ideological background of Buddhism in which its key-concepts as found in other sources have been traced, identified and documented. The traditional substrata of the Buddhist mythology have also been explored from the pre-vedic, vedic, puranic, regional and tribal sources. It has been argued that the doctrinal, epistemological and ontological critique of Buddhism vis-a-vis the standpoints of the Jains, Vedantists, M?m?{msakas and Ny?ya-Vai?e]sikas clearly suggest that Buddhism was viewed by its opponents as a thought-complex and not as a distinct religious system.It has also been pointed out how factionalism arising out of personality clashes eventually led to doctrinal centrifugality. The last chapter deals with the final transformation of Buddhism with reference to its basic character as the crucible for generating various ideas and practices. It has been stressed that the period which has been stigmatized by most historians as that of the decline and disappearance of Buddhism was in reality the only period in its long history in India in which it was able to come out of its dry academic shell and renovate all the existing traditional and popular spiritual disciplines by its own spirit.A long appendix on Buddhist iconography further enriches this path-breaking work.