This chapter discusses the history of science and scientists in the Great War. Few historians have tried to deal with the implications of scientific mobilisation for understanding of the conflict and its consequences. The Great War created opportunities for the systematic application of a new vocabulary of warfare, a new set of professional specialities, a new emphasis on the role of women and minorities, as well as a new politics of science. Scientific internationalism was one of the casualties of the war for civilisation. The war produced many changes in science and its relationship to society. At the same time, the war gave new depth and meaning to the relationship between science and the military. If people are to read it correctly, they must revisit those four years when scientists across the world chose to serve the political order they had helped to create.