The Responsibility to Protect (R2P) norm is designed to reduce, if not eliminate entirely, mass atrocity crimes, and norm entrepreneurs have achieved some notable successes in their attempts to promote it. But they have also faced significant resistance from norm antipreneurs. This chapter first describes the normative status quo which R2P entrepreneurs are trying to modify – and which antipreneurs are defending – namely, the relatively strict traditional interpretation of sovereignty, before the challenge R2P poses to it is examined. Most of the chapter then examines resistance to R2P, organised according to a strategic/ tactical resistance distinction; strategic resistance, or the justifications given for resisting the new R2P norm, is considered first, then tactical resistance – the discrete frustrating or blocking moves antipreneurs make in particular institutional contexts – is then considered. The chapter finishes with several conclusions. Empirically, because it is found that the effort to diffuse and entrench R2P’s Pillar III faces fierce resistance, the chapter ultimately concludes that R2P is currently stalled and is suffering from ‘arrested development’. Theoretically, it is found that distinguishing between norm entrepreneurs and antipreneurs is conceptually useful because it alerts scholars to the strategic and tactical advantages which accrue to antipreneurs in contexts, like the R2P case, in which the normative status quo is deeply entrenched and institutionalised. And finally, because theorising systematically about antipreneurs can reveal these asymmetric antipreneurial advantages, R2P entrepreneurs who take heed may be able to more skilfully adjust their future efforts to advance the norm.