On September 9, 2013, diplomats and civil society activists gathered in a ballroom in New York to welcome Jennifer Welsh as the UN Secretary-General's new Special Adviser on the Responsibility to Protect (RtoP). In her first public appearance in that role, Special Adviser Welsh explained that one of her top priorities would be “to take prevention seriously and to make it meaningful in practice.” “In the context of RtoP,” Welsh added during the discussion, “we are talking about crimes, and crimes have implications in terms of how we deal with them. You'll hear me say that a lot.” Welsh's approach of treating RtoP as a principle that is primarily concerned with prevention and is firmly linked to international crimes neatly captures the evolution of RtoP since its formal acceptance by states at the 2005 UN World Summit. Paragraphs 138 to 140 of the World Summit's Outcome Document not only elevated the element of prevention to a prominent place within the principle of RtoP but also restricted the scope of RtoP to four specific crimes under international law: genocide, war crimes, ethnic cleansing, and crimes against humanity. The crime and prevention–focused version of RtoP has subsequently been defended and promoted by Secretary-General Ban Ki-moon and by UN member states. This article seeks to systematically explore some of the implications of linking RtoP to the concept of international crimes, with a particular focus on the preventive dimension of RtoP, the so-called responsibility to prevent. What, then, are the consequences of approaching the responsibility to prevent as the prevention of international crimes?In order to systematically examine this question, this article turns to literature from criminology. While the criminological perspective has so far been neglected in debates on RtoP, the prominent criminologists John Hagan and Wenona Rymond-Richmond argue vehemently that “criminology is crucially positioned to contribute understanding and direction to what the United Nations has mandated as the ‘Responsibility to Protect’ groups that are threatened with mass atrocities.” For the purpose of this article, the label “criminology” comprises domestic criminology, supranational criminology, and international criminal law. While insights from supranational criminology and international criminal law are directly applicable to international crimes, translating knowledge generated in relation to crimes at the domestic level to atrocity crimes at the international level is, of course, not without challenges. Reasoning by analogy is an important method in this regard, though given the anarchical nature of international society some analogies will inevitably be imperfect. The benefits of such an approach, if carefully employed, however, outweigh the risks.