This book is based on the Sir Hersch Lauterpacht Memorial Lectures which I delivered in Cambridge in January 2008. Although a number of changes and additions have been made in order to conform to the book format, overall I have attempted to maintain the style and feel of the Lectures.

I am grateful to Sir Elihu Lauterpacht for his invitation to take part in the Lecture Series and to his colleagues in the Lauterpacht Centre for the support and warm hospitality that was extended to me. My thanks go particularly to Professor James Crawford, Anita Rutherford, Kirsten Hollis and Michelle Bradfield.

I owe an intellectual and personal debt of gratitude to many former colleagues in the United Nations Secretariat who directly or indirectly contributed to the collective endeavour that is described in this book. They are too numerous to name but they will recognize their role in the narrative of events. I must, however, single out for special recognition the two who held the office of Legal Counsel of the United Nations during the period when these events took place and who gave their imprint to the legal advice that forms the spine of this book: the late Carl-August Fleischhauer and Hans Corell. Each of them brought a distinctive legal philosophy and personality to bear on the issues that confronted them and each carried on the great tradition of the international civil service and of the rule of law that had been espoused by their predecessors.