This paper explores the origins of the Responsibility to Protect (R2P) principle within the contemporary history of armed humanitarian intervention. By reviewing legal and political scholarship surrounding the concept of R2P and its application, this paper uses a constructivist lens to argue that R2P failed to be adopted as a principle of customary international law due to its normative and legal ambiguity. This paper concludes with a critical examination of R2P's first, and likely final, invocation during the Libyan crisis of 2011.