perhaps there is no better way to introduce this book than to explain its title. The choice of the plural form “theories” is of course deliberate, intending to convey the distinct message that the present field of enquiry is by no means reducible to a monolithic set of ideas divorced from various historical processes. A central aim of the book is then to show that uṣūl al-fiqh, the theoretical and philosophical foundation of Islamic law, constituted an umbrella under which synchronic and diachronic variations existed. The plan of the book manifests this concern for unraveling the most essential features of these variations. In the first chapter, I discuss the evolving principles of jurisprudence, from their rudimentary beginnings down to the end of the third/ninth century, when uṣūl al-fiqh came into existence as an integral legal methodology. Of the three centuries covered in this chapter, the second receives a treatment that is largely in agreement with the conventional understanding in the field, an understanding first propounded by Joseph Schacht. With regard to the first/seventh and, especially, the third/ninth centuries, I offer a generally different interpretation. In the case of the first century, I subscribe neither to the traditional view that Islamic law, as a more or less mature system, began during or immediately after the lifetime of the Prophet, nor to the relatively recent view which places the rudimentary beginnings of this law around the end of the first century of the Hijra (ca. 715 a.d.).