Gratian's Decretum is not one book, but two. The Decretum that has been known until now was preceded by another, much shorter book, which was almost entirely subsumed into the later version. This explains many of the mysteries that have surrounded the Decretum and that have hampered study of this pivotal text. It also raises new questions, about the authorship of the Decretum, about the environment in which its author or authors worked, and about the development of legal science and scholasticism in the twelfth century. This book could only begin to address those questions.

Gratian's Decretum is often quoted, cited, and discussed in the scholarly literature treating various aspects of the middle ages. Authors of such studies are now invited to introduce another level of complexity into their work. The discovery of the first recension will, in the first place, facilitate study of the Decretum for those scholars who simply want to explore Gratian's standpoint on some specific issue. The Decretum, as known from Friedberg's edition, is not an easy book to approach or to understand. The second recension introduced much new material which was not synthesized into a coherent whole, although the additions, had their implications been worked out, would frequently invalidate or modify the synthesis achieved in the first recension. The result is that the more carefully a modern scholar reads the Decretum, the more confused and confusing it appears.