Shiʿi Muslims have played a crucial role, proportionally greater than their relative size, in furthering the civilizational achievements of Islam. Indeed, the Shiʿi scholars and literati of various branches and regions, including scientists, philosophers, theologians, jurists and poets, have made seminal contributions to Islamic thought and culture. There have also been numerous Shiʿi dynasties, families or individual rulers who patronized scholars, poets and artists as well as various institutions of learning in Islam. In spite of its significance, however, Shiʿi Islam has received little scholarly attention in the West, and when it has been discussed, whether in general or in terms of some of its subdivisions, it has normally been treated marginally as a ‘sect’ or a ‘heterodoxy’. The present book draws on the scattered findings of modern scholarship in the field, attempting to explain the formative era of Shiʿi Islam, when a multitude of Muslim groups and schools of thought were elaborating their doctrinal positions. Subsequent chapters are devoted to the history of the Ithnaʿasharis, or Twelvers, the Ismailis, the Zaydis and the Nusayris (now more commonly known in Syria as the Alawis), the four communities that account for almost the entirety of the Shiʿi Muslim population of the world. The result is a comprehensive survey of Shiʿi Islam that will serve as an accessible work of reference for academics in both Islamic and Middle Eastern studies, as well as the broader field of the History of Religions, and also more general, non-specialist readers.