How has contemporary humanitarianism become the dominant framework for how states construct their moral obligations to non-citizens? To answer this question, this book examines the history of humanitarianism in international relations by tracing the relationship between transnational moral obligation and sovereignty from the 16th century to the present. Whereas existing studies of humanitarianism examine the diffusion of such norms or their transmission by non-state actors, this volume explicitly links humanitarianism to the broader concept of sovereignty. Rather than only focusing on the expansion of humanitarian norms, it examines how sovereignty both challenges and sets limits on them. Humanitarian norms are shown to act just as much to reinforce the logic of sovereignty as they do to challenge it. Contemporary humanitarianism is often described in universalist terms, which suggests that humanitarian activity transcends borders in order to provide assistance to those who suffer. In contrast, this book suggests a more counterintuitive and complex understanding of moral obligation, namely that humanitarian discourse not only provides a framework for legitimate humanitarian action, but it also establishes the limits of moral obligation. It will be of great interest to a wide audience of scholars and students in international relations theory, constructivism and norms, and humanitarianism and politics.