Between 1945 and the mid-1970s, international and European norms of sexual non-discrimination had virtually no impact on state behaviour, both because international and regional bodies had no expectations that states would comply with these or any other human rights norms, and because states refused to take the initiative to incorporate systemic norms in the absence of any external pressure. In a process apparent since about the mid-1970s, international and regional bodies have expanded and strengthened legal regimes regarding sexual non-discrimination and established concrete measures of implementation. They have also developed detailed ‘how to’ sets of instructions in the form of action plans or programmes specifying the requisite legislative and public policy action to be taken by states.1 This international regime strengthening, in turn, has exerted pressure on states to modify their practices accordingly. Yet while regime strength is by itself a necessary condition for diffusion, it is not sufficient to explain either the variance in state responses to systemic norms of sexual non-discrimination or the limited overall impact these norms have had on state behaviour. Whether or not a state incorporates systemic norms of sexual non-discrimination depends also on the strength of the gender-biased corporate identity of the state, the degree of international political will to use existing monitoring and enforcement resources, and the effectiveness of domestic feminist activism and private individual litigation. The explanation for why states respond differently to systemic norms of sexual non-discrimination lies in the complex interplay between these various structures and agents, and the best way to capture this dynamic, I suggest, is to draw on some of the core ideas associated with critical realism.