Imam Muhammad al-Baqir was one of the most erudite Muslims of his age and played a significant role in the history of early Islam. At once a versatile leader and scholar, he was also an authority on the exegesis of the Qur"an, the traditions of the Prophet, and all matters relating to the rites, rituals, and practice of Islam. Using hitherto largely ignored Shi"i sources, Arzina R. Lalani explores al-Baqir"s pivotal contributions to Islamic thought in its early formative period, contributions that were powerfully to affect developments in Shi"a law, theology, and religious practice. This study gives particular attention to al-Baqir"s vital role in the formulation of the function and nature of the self.