By comparing two eras of European heads-of-state-or-government (HoSG) summitry – the summits of 1961 and those between 1967 and 1974 – an under-studied factor in the European Council’s institutionalisation is revealed. At the 1961 summits, political integration dominated HoSG discussions, whereas from 1967 onward, economic reform – in the form of the common market, common agriculture policy, economic and monetary union and regional development fund – was the dominant topic of discussions. The institutionalisation of summitry was a product not only of personalities and international events but also of the mechanism of continuous negotiation on economic reform.