The study of how new norms are implemented has been neglected within constructivist theorizing. The assumption is that once a new norm is institutionalized, the analytical ‘job is done’. Yet the same levels of institutionalization of a given international norm can be observed across states but with radically different outcomes in terms of practice. This observed ‘institutionalization-implementation gap’ matters because it shapes whether important international norms make any difference in terms of outcome. Consequently this conceptual chapter argues that it is useful to analytically distinguish between two distinct processes: ‘institutionalization’ as an international process and ‘implementation’ as a domestic process. This clarity of distinction is important for two reasons. First, it enables a clear distinction between two distinct phases of political contestation. Second, it enables exploration of why, in spite of similar levels of institutionalization, there is often significant variation in the way in which norms and organizations play out in practice.