A significant amount of International Relations scholarship examines the role of international norms in world politics. Existing work, though, focuses mainly on how these norms emerge and the process by which governments sign and ratify them. In conventional accounts, the story ends there. Yet, this tells us very little about the conditions under which these norms actually make any difference in practice. When do these norms actually change what happens on the ground? In order to address this analytical gap, the book develops an original conceptual framework for understanding the role of implementation in world politics. It applies this framework to explain variation in the impact of a range of people-centred norms relating to humanitarianism, human rights, and development.