The responsibility to protect (R2P) is often referred to as a new concept on the basis that it provides both states and the international community re- sponsibilities, rather than merely rights, to protect populations from mass atrocities. As this article argues, this claim of novelty is overstated. And yet, R2P has comprised an important development in human protection over the past two decades: it has helped to generate a degree of consensus on how to prevent and address atrocity situations. If R2P is not as novel as is often suggested, why has it had such an impact on international dis- course? After demonstrating R2Pâ€™s overstated novelty, this article advances four key factors that help explain its meaningful international impact: the importance of previous and contiguous normative developments, the role played by norm entrepreneurs, the emphasis placed on prevention over intervention, and the conceptâ€™s constructive mix of clarity and ambiguity. By doing so, it provides a stronger understanding of the norm.