This study attempts to analyse the world of thought presented in the Kathavatthu. It seeks to elucidate the controversies presented in this text in the light of the historical development of Buddhist thought and its wider milieu. It not only seeks to analyse the doctrinal significance of the points discussed but to connect them historically with specific tendencies in the growth of the Buddhist faith, practice and organisation. It further seeks to correlate Buddhist developments with similar developments in other contemporary schools. Besides the Kathavatthu, the author has tapped almost all relevant sources e.g. other Pali canonical and non-canonical works, treatises of Vasumitra, Bhavya and Vinitadeva on eighteen Buddhist sects, Chinese travellers accounts, and extant works of the Buddhist sects. An authoritative and insightful study that should interest scholars of Buddhism all the world over.