This chapter describes the debate about the UK's world role into historical context, assessing different ways of understanding the UK's international power and the changing ways in which UK leaders have conceptualised and justified a 'great' role for the UK in the global arena. It explores the history and legacy of the UK's key international relationships, focusing on its membership of key international organisations: the United Nations, the European Union, North Atlantic Treaty Organization, the Organization for Security and Co-operation in Europe and the Organisation for Economic Co-operation and Development. One hallmark of the 'sovereignty' debate in Britain has been the tendency to reduce it to what is known as a zero-sum game. In the first and by far the longest period, the big ideas about the UK's role in the world took shape and entrenched themselves within the political class and public mind at large.