It will be convenient to state what this book is and what it is not. It is far from being a comprehensive statement of Roman law and common law comparatively treated. It is rather a comparison of some of the leading rules and institutions of the two systems. One of us many years ago produced a small book entitled Equity in Roman Law, the aim of which was to show the way in which the Roman lawyer worked. The institutions with which he dealt were subordinated to the way in which he worked on them, and an attempt was made to show that, working on institutions often very differently shaped, he handled them in ways very similar to those of English lawyers and reached results, especially in the field covered by modern English equity, astonishingly like theirs. In this book, on the other hand, it is the rules and institutions themselves that are compared. These are no doubt to some extent the work of the lawyers, but that is not true of the most basic notions: these were formed in their essentials long before there was such a thing as the professional study of law. They may be regarded as given, as not being the lawyers' work but the materials on which they worked, moulded however into the form in which we know them from the sources by many generations of lawyers and, no doubt, politicians.