Alongside the individual rules of God’s law (shari?a), 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 shari?a? The answers to these questions have been debated and discussed by Muslim scholars in the genre of literature called u?ul 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 Shi?ite tradition of Islamic thought (Zaydi, Isma?ili and Twelver). A careful side-by-side reading of these texts and commentaries will help identify themes peculiar to the Shi?ite "family" of legal theories. The distinctive Shi?ite contribution to the history of u?ul 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 Shi?ite u?ul to the wider field.