Transnational counter-terrorism is a crowded field dominated by closed institutions. They include formal international organisations, informal international or multilateral institutions, hybrid entities, private actors, and regional organisations. National authorities and states are also part of this transnational milieu, implicated as members of international organisations and institutions, as founders and funders, as co-ordinators, and as implementers. This chapter argues that consideration of institutions is critical to achieving insight into the dynamics of transnational counter-terrorism, and in particular to understanding the flows of power, norms, and activity across different scales of transnational counter-terrorism, as well as from counter-terrorism to other fields of activity. It then considers the institutions of transnational counter-terrorism: the UN Security Council and its subordinate entities, the General Assembly, the members of the Global Counter-Terrorism Coordination Compact, and informal institutions, organisations, hybrids, private actors, and others that have been drawn into the transnational counter-terrorism order.