This book explains why there is a pronounced disjuncture between R2P's habitual invocation and its actual influence, and why it will not make the transformative progress its proponents claim. Rather than disputing that R2P is a norm, or declaring that norms are insignificant, Hehir engages with post-positivist constructivist accounts on the role of norms to demonstrate first, that the efficacy of a norm is not directly related to the extent to which it is proliferated or invoked, and second, that in the post-institutionalization phase, norms undergo both contestation and (potentially regressive) reinterpretation. This volume analyses the evolution of R2P, and demonstrates that it has been steadily circumscribed and co-opted, so that today it has no power to meaningfully influence the behaviour of states. It is essential reading for academic audiences in the disciplines of International Relations and International Law.