This book is the result of a research project funded by the Swiss National Science Foundation (Grant 116148) with the support of the Geneva Academy of International Humanitarian Law and Human Rights. As everyone who has ever written a book knows, producing an academic work is far from a lonely endeavour. In this case in particular, as this book is the final product of a research project involving a number of people over several years, it was in many ways a collective effort. I owe no small debt of gratitude to many colleagues and friends. First and foremost, the intellectual and institutional support that Marco Sass?li provided laid the foundations for this work and made it possible to see the project through to completion. His vision and his approach to IHL have inspired and underpinned this study in many ways, and his willingness and extraordinary ability to engage with the finer points of any legal argument have certainly improved this work. I cannot thank him enough for his commitment and dedication. It has been a delight, an honour and a privilege to work with him at the University of Geneva for a number of years. I am very grateful to Vincent Chetail for having initiated the project with Marco and for having included me in it. I have learned much through our fruitful collaboration.