Mémoire sur les Carmathes du Bahraïn et les Fatimides (A study of the Carmatians of Bahrain and the Fatimids) is a history of two Shia political and theological movements that shook the Islamic world between the ninth and 12th centuries. Both the Carmatians (also seen as Qarmatians or Karmathians) and Fatimids were offshoots of mainstream Shia Islam. While each looked to the descendants of ‘Ali ibn Abi Talib (died 661) for spiritual and temporal leadership, they differed over the line of descent to be followed. The Carmatians established their power center in the northeastern Arabian Peninsula and on the islands of Bahrain. They were finally eclipsed in the 1070s after a period of rivalry with the Fatimids in Cairo and the Abbasids in Baghdad. The Fatimids, on the other hand, made a larger contribution to the Islamic cultural legacy and posed a more permanent threat to Baghdad. Their empire arose in Algeria and Tunisia in the early tenth century. Eventually, they established their capital in Cairo, where a Fatimid caliph ruled until the last of the line died out in the mid-12th century. This book is the first volume of Michael Jan de Goeje’s series Mémoires d’h̓istoire et de géographie orientales (Studies on Oriental history and geography). Orientalist research of the period is generally characterized as the study of the Islamic Middle East, particularly the early and medieval periods, by scholars rooted in the philological and textual traditions. Its goals were revolutionary at the time, namely to correct the unfortunate “cleavage between Orientalists and [Western] historians—as though there were two kinds of humanity and not a common history,” in the words of French scholar Jean Sauvaget. De Goeje was a standard-bearer of this early revolution. He concentrated on the editing of Arabic historical and geographical texts. Mémoire sur les Carmathes du Bahraïn et les Fatimides is one of his few excursions into analysis. In his interpretation, the Fatimids played a larger role in Carmatian ideology and politics than more recent research has supported. From his position as librarian for manuscripts at the University of Leiden, he supervised the editing of al-Tabari’s monumental Tarīkh al-Ṭabarī (The history of al-Tabari), a project that took 22 years and covered 10,000 pages. He was the first general editor of the Encyclopaedia of Islam.