This study emphasizes the legacies of British internationalism in the international organizations of the twentieth century while examining British responses to the end of the British Empire. After the First and Second World Wars, the victorious powers established international organizations such as the League of Nations and the United Nations in an attempt to institutionalize peace. The staff of these bodies became known as the international civil service, which pledged loyalty to the aims of the organization rather than their home government. For much of the twentieth century, Britons were the most or second- most represented nationality in the international civil service. Why did so many Britons participate? This book shows how British planners at the League based the international civil service on the British civil services, and how subsequent British governments encouraged high rates of participation as a way to project influence and goodwill as the British Empire declined. This book will appeal to scholars of internationalism and modern history at the undergraduate and graduate levels, as well as specialists and international civil servants themselves.