This book is an outcome of the research project entitled, ‘The emerging international constitutional order: the implications of hierarchy in nternational law for the coherence and legitimacy of international decision-making’. The project was embedded in the Amsterdam Center for International Law, University of Amsterdam, under the leadership of Erika deWet, and funded by the Netherlands Organisation for Scientific Research. From the outset of this book, we greatly benefited from the involvement of our Amsterdam colleague Yvonne Donders and the PhD researchers on the project: Lisa Clarke, Stephan Hollenberg, and Louwrens Kiestra. Their suggestions, criticism, team spirit, sense of humour, support, patience, and occasional impatience made our daily research routine a truly enjoyable experience. We also received invaluable comments from other Amsterdam colleagues: Catherine Brölmann, Jean d'Aspremont, Christina Eckes, Pieter Jan Kuijper, and André Nollkaemper. We are thankful to Brechtje Vossenberg for her research assistance, Belinda Macmahon for proofreading and editing the manuscript, and Carly Vidmar for being our informal consultant in linguistics. We are also indebted with the anonymous reviewers of the Oxford University Press for constructive criticism and very helpful suggestions. The book further benefited from workshops organized in the framework of the COST Action No IS0602, sponsored by the European Science Foundation. We are especially thankful to Aristoteles Constantinides for his thoughtful insights during these meetings. Our lives would have been miserable without the administrative support of Eric Breuker, Martine van Trigt, and José Visser. It is a coincidence that twothirds of our administrative aides also had their own research interests in one of the potentially hierarchically superior norms of international law. Lastly, we would like to thank the contributors to this book for being a truly pleasant group to work with; for reading and commenting on one nother's draft chapters; for being open for discussion and suggestions; and for respecting the rather strict deadlines.