This collection of essays has its origin in a conference which we organised at Christ's College, Cambridge in April 1999. The aims of the conference are explained in our introductory chapter. Here it is enough to say that, while unjustified enrichment has clearly been one of the most intellectually vital areas of private law over the last decades, there seemed to us to be scope for comparative exploration of the area in a manner more comprehensive than it had until then received. With this in mind we invited a small group of speakers to Cambridge, where at the time we were both teaching. Our invitations to contributors were perhaps unusually prescriptive, and in particular allowed them no choice of topic. The main reason for this was that for each topic we wished to have two papers, each taking a different perspective. So we are extremely grateful to the contributors both for their enthusiastic participation in the conference and for preparing the papers published here. We would like also to acknowledge the helpful guidance of Peter Birks during the planning phase of the conference. In addition we warmly thank the chairmen who presided over the various sessions of the conference: Lord Goff of Chieveley, Lord Hope of Craighead, Professor Gareth Jones, Lord Rodger of Earlsferry, Professor Peter Schlechtriem and Lord Steyn.

The manuscripts for this book were submitted by the end of 1999; they therefore reflect the law at that date.