The intellectual trajectory from which this book grew owes much to my interactions and collaborations with fellow students, instructors and colleagues, and my own students over the years. The question of ethics in world politics has been my abiding intellectual interest since my master's degree at Carleton University, where I wrote a thesis on the ethics of strategic defences. Fen Hampson, an International Relations scholar, and Tom Darby, a political theorist, generously humoured my immature probings into a subject that didn't really fit in either discipline as commonly practised, particularly when I ventured astray from traditional moral philosophy and into interpretive approaches to ethics, the philosophy of technology and other terrain that was quite exotic for a subject traditionally under the ambit of strategic studies. As I look back upon that project, I see this volume in many ways as the logical and (hopefully) more mature outcome of that earlier, less self-conscious and more inchoate attempt to bridge philosophy, ethics and politics. Peter Katzenstein, Henry Shue and Judith Reppy subsequently lent their essential support to an interpretive and structural approach to understanding moral norms in world politics for my Ph.D. dissertation, later a book, which examined the chemical weapons taboo from a genealogical perspective. The move from interpretivism to constructivism, and later from structure to agency, occupied the next stage of my intellectual agenda, one that was particularly and powerfully influenced by my interactions with my fellow students at Cornell, colleagues encountered through Peter Katzenstein's Culture of National Security project and elsewhere, and colleagues and students at the University of Minnesota.