Hedley Bull put institutions on the map for the English school, and his set of five institutions of ‘international’ (= interstate) society (diplomacy, international law, the balance of power, war, and the role of great powers) occupies the whole central third of his 1977 book. Following on from Bull, the concept of institutions has been central to English school thinking for three reasons: First, because it fleshes out the substantive content of international society, second, because it underpins what Bull and other English school writers mean by ‘order’ in international relations (IR), and third, because the particular understanding of institutions in English school thinking is one of the main things that differentiates it from the mainstream, rationalist, neo-liberal institutionalist, study of international regimes (Keohane, 1988, Hurrell, 1991, Evans and Wilson, 1992, Buzan, 1993, Waever, 1998:109–12, Alderson and Hurrell, 2000a).