This article is a revised and expanded version of my inaugural lecture as Dixie Professor of Ecclesiastical History at the University of Cambridge, delivered on 12 March 2014. It highlights the evolution of Ecclesiastical History to include the study of Christianity in the global south and shows how recent developments in the study of African and world history have produced a dynamic and multi-faceted model of religious encounter, an encounter which includes the agency of indigenous Christians alongside the activities of missionaries. Investigating the contribution of faith missionaries to the production of colonial knowledge in Belgian Congo, the article challenges stereotypes about the relations between Pentecostalism and modernity, and between mission and empire. Throughout, consideration is given to the range of missionary sources, textual, visual, and material, and their utility in reconstructing social differentiation in African societies, particularly in revealing indigenous African criticism of ‘custom’.