Alongside the individual rules of God's law (sharīʿa), there has been a vibrant history of more philosophical or theoretical discussions in Islamic thought. Where does God's law come from? How are God's rules to be discovered for situations not covered in the revealed sources? Who, within the Muslim community, can make a valid pronouncement on the content of the sharīʿa? The answers to these questions have been debated and discussed by Muslim scholars in the genre of literature called uṣūl al-fiqh, glossed in English language secondary literature as "Islamic legal theory". This volume contains editions and commentaries of hitherto un-edited manuscripts from the various strands of the Shiʿite tradition of Islamic thought (Zaydi, Ismaʿili and Twelver). A careful side-by-side reading of these texts and commentaries will help identify themes peculiar to the Shiʿite "family" of legal theories. The distinctive Shiʿite contribution to the history of uṣūl al-fiqh has not received the attention it deserves in contemporary scholarship; this volume forms part of wider attempt to bring the richness and diversity of Shiʿite uṣūl to the wider field.