This book examines the moral dilemmas of nuclear proliferation, and the justifications of both nuclear pursuit and avoidance by contemporary states. The work analyses a core set of moral dilemmas with political and policy import that ensnare decision-makers amongst state and non-state nuclear aspirants, as well as amongst states committed to preventing horizontal proliferation. It shows that these dilemmas' character, structure, and implications have not yet been adequately understood or appreciated, and that such an understanding is necessary for an effective set of nonproliferation policies. Further, the book shows that the dilemmas' force and political policy import are evident in the 'discourses' that diverse actors undertake to defend their nuclear choices, and how the dilemmas of nuclear aspirants are implicated in those of nuclear preventers. The author concludes with policy recommendations that reinforce some already made by scholars and experts and others that advise significantly different courses of action. This book reveals how the moral dilemmas of nuclear aspiration, avoidance, and prevention constitute the security dilemmas and paradoxes that comprise much of the 21st century security environment. This book will be of much interest to students of nuclear proliferation, international relations, ethics, and international security studies.