The Ismāʿīlīs constitute the second largest Shīʿī community after the Twelvers in the Muslim world and are now scattered in more than twenty countries of Asia, Africa, Europe and America. This book traces the history and doctrines of the Ismāʿīlī movement from its origins to the present time, a period of approximately twelve centuries.

The origins of Sunnism and Shīʿism, the two main divisions of Islam, may be traced to the crisis of succession faced by the nascent Muslim community following the death of the Prophet Muḥammad, though the doctrinal bases of these divisions developed gradually in the course of several centuries. In time, Shīʿī Islam, the minoritarian view, became subdivided into different groups, many of which proved short-lived. But Imāmī Shīʿism, providing the common early heritage for several Shīʿī communities, notably the Twelvers and the Ismāʿīlīs, was a major exception.

The Ismāʿīlīs have had a long and eventful history. In medieval times, they twice established states of their own and played important parts for relatively long periods on the historical stage of the Muslim world. During the second century of their history, the Ismāʿīlīs founded the first Shīʿī caliphate under the Fāṭimid caliph-imams. They also made important contributions to Islamic thought and culture during the Fāṭimid period. Later, after a schism that split Ismāʿīlism into its two major Nizārī and Mustaʿlian branches, the Nizārī leaders succeeded in founding a cohesive state, with numerous mountain strongholds and scattered territories stretching from eastern Persia to Syria.