Pieter Jan Kuijper is Professor of the Law of International Organizations in the Amsterdam Centre of International Law (ACIL), University of Amsterdam. He previously worked for the European Commission, most recently as Principal Legal Advisor and Director of the External Relations and Trade Law team of the Commission Legal Service. He has also been Director of the Legal Affairs Division of the WTO Secretariat (1999 2002). His publications have concentrated on EU law, WTO law and general international law and the relationship between them.