Al-Milal wan-Nihal (Religions and Sects)

الملل والنحل

A pioneering work of comparative religion and heresiography. Ash-Shahrastani systematically catalogs and describes the beliefs of Islamic sects, other Abrahamic religions, ancient Greek philosophies, and Indian religions. His methodology of presenting each group's beliefs from their own perspective, rather than merely refuting them, was remarkably objective for its time and makes this work a foundational text in the study of religions.