This book addresses an often neglected question in the field of European Private Law: to what extent is there a need for unification of contract law in Europe? This question is not only important in view of the recent Communications on European contract law that were issued by the European Commission. It also provokes the pertinent issue whether diversity of (contract) law is actually a barrier to the proper functioning of the European internal market. In order to answer these questions, this book adopts an interdisciplinary approach: not only law, but also insights from (behavioural) economics and psychology are taken into account.The contributors to this volume are Gerhard Wagner, Helmut Wagner, Jaap Hage, Heico Kerkmeester, Jeffrey J. Rachlinski, Thomas Wilhelmsson and Jan Smits.