The authority–legitimation link states that international institutions exercising authority need to nurture the belief in their legitimacy. The authority–legitimation link points to fundamental challenges for the global governance system: with the rise of international authorities that are, at the same time, more intrusive, state consent is undermined and societies are affected directly. Consequently, legitimation problems arise, followed by processes of delegitimation, which then trigger responses by the challenged institutions. Using concepts of historical institutionalism, it is argued in this chapter that the authority–legitimation link produces reactive sequences either via the route of societal politicization or via counter-institutionalization by states. These reactive sequences may result in either a decline or a deepening of global governance depending on the responses of authority holders.