Since the late nineteenth century, the historical dynamics of internationalisation and transnationalisation of imperial and colonial affairs have been numerous and consequential, leading to a significant increase in the production, circulation and institutionalisation of common instruments for formulating and evaluating imperial and colonial policies. Empire states and colonial administrations sought to respond to these challenges and opportunities. So did other organisations, some of them closely linked to colonial situations. Focusing on different chronologies (but marked by some continuities), from the League of Nations to the United Nations, this paper looks at different groups and expressions of 'religious internationalism' addressing the opportunities and respond to the constraints of the internationalisation and transnationalisation of imperial and colonial affairs, and related norms, programmes and policies on a number of topics. Drawing on Catholic and Protestant cases and highlighting a range of relevant themes, from colonial labour to development and racism, the paper examines the Union Catholique d'Études Internationales (1920), the Department of Social and Economic Research of the International Missionary Council (1929), the Commission of the Churches on International Affairs of the World Council of Churches (1946), the National Catholic Welfare Conference General (NCWC) and its Office for United Nations Affairs (1946), the North American Assembly on African Affairs (1952), the Programme to Combat Racism of the World Council of Churches (1969) and the influence of Économie et humanisme in the developmental thinking of the Organization for Economic Cooperation and Development in the 1970s.