This dissertation examines the role that German Protestant missionaries from the Rhenish Mission Society played in the conquest of the Herero and the development of German colonialism in late nineteenth- and early twentieth-century South-West Africa. Furthermore, it explores how missionaries' interaction with colonialism influenced their articulation of the missionary project. As the objects of missionary evangelization and the subjects of colonial policy, the Herero were integral to debates between missionaries and colonial officials about the nature of colonialism. Missionaries and colonial officials attempted to instrumentalize each other in order to achieve their own aims as they negotiated the place of the Herero in the colonial order, resulting in a reciprocal process in which the missionary and colonial projects influenced each other. This study focuses on a tumultuous period in which Germany conquered the Herero and assimilated them into South-West Africa as a subject people. It begins with a biological catastrophe that decimated Herero herds, impoverishing the Herero and forcing them to sell land to settlers, which threatened the basis for Herero economic and political autonomy. It continues with the Herero war of 1904 to 1907, in which Germany nearly annihilated the Herero. It ends with the close of the war and the drafting of regulations that attempted to order African life according to the imperatives of settler colonialism. Missionaries to the Herero were present at every stage of the conquest of the Herero and the consolidation of colonialism in the territory. At times contesting, at other times cooperating with the colonial regime, the missionaries attempted first to regulate Herero contact with colonialism, and then, in aftermath of war, to integrate them into the colonial order. Through negotiation with the colonial government, the missionaries reimagined the nature of mission work and shaped the practice of colonialism in South-West Africa.