The bulk of the original text of this book was completed by the mid 1980s. After some minor additions, the first edition of the book was published in 1990. As the first comprehensive history of the Ismāʿīlīs, synthesizing the scattered results of modern scholarship in the field, this publication was well received by the academic community as well as the Ismāʿīlīs worldwide. As a result, it was reprinted several times, in addition to being translated into Arabic, Persian, Urdu, Turkish and Tajik (Cyrillic). The Persian translation of The Ismāʿīlīs: their history and doctrines also received the ‘best book of the year award’ in the Islamic Republic of Iran, an unexpected accolade.

Meanwhile, in 1988 I had joined The Institute of Ismaili Studies in London, which serves as an international forum for Ismāʿīlī studies. The progress in this field of Islamic studies has proceeded at an astonishing pace during the last two decades, as reflected in my Ismaili literature: A bibliography of sources and studies (2004), while my own Ismāʿīlī scholarship has moved beyond its initial stages in the 1960s and 1970s. All this has necessitated the production of a second revised edition of this book. In this new edition, many parts of all chapters have been re-written or otherwise revised, and much new material has been incorporated throughout the text of the book. In addition, doctrinal expositions and interpretations have been sharpened to reflect more recent academic perspectives on aspects of Ismāʿīlī thought.