Thirtheen years after its publication in Italian, the presentation of this book to an English-speaking readership provides an opportunity for some new reflections and the presentation of further information in order to bring it up to date. The book introduces the reader to the various legal systems of the middle ages, and at the same time explains the individual complexities of these systems. In doing so, it aims to facilitate individual research into specific issues. It does not, however, consider in detail the various juridical institutions. Apart from a few digressions, neither does it deal with the private and public law of the time, even in the context of the most important and delicate matters. However, careful reading of the book should make the ancient texts more easily accessible to the reader. In effect, the book offers a compass by which to navigate the subject-matter. One needs to take special care when addressing what is written in the sources. It is always tempting to believe that a problem exists if and when such a problem appears to be revealed through the laws or by jurists. It is also all too easy to believe that no problem exists if no reference is made to it. As is the case in the field of theology, juridical doctrine has traditionally been extremely sensitive to contemporary problems. However, it is also the product of a series of specialized wisdoms, based on particular sources and governed by internal rules that influenced discussion, and were consequently able to shape doctrine according to abstract notions. On the ground, though, the realities were often somewhat different, or engaged in addressing certain issues earlier or to a greater extent than it would appear if one focuses on those matters that dominate university discussions.1 This is often the case even today, despite the fact that we are now governed by sources of knowledge that are less rigid than those of the past.