Mahdis and Millenarians is a discussion of Shiite groups in eighth- and ninth-century Iraq and Iran, whose ideas reflected a mixture of indigenous non-Muslim religious teachings and practices in Iraq in the early centuries of Islamic rule and demonstrates the fluidity of religious boundaries of this period. Particular attention is given to the millenarian expectations and the revolutionary political activities of these sects. Specifically, the author's intention is to define the term 'millenarian', to explain how these groups reflect that definition, and to show how they consequently need to be seen in a much larger context than Shiite or even simply Muslim history. The author concentrates, therefore, on the historical-sociological role of these movements. The central thesis of the study is that they were the first revolutionary chiliastic groups in Islamic history and, combined with the later influence of some of their doctrines, contributed to the tactics and teachings of a number of subsequent Shiite or quasi-Shiite sectarian groups.