The impact of air raid precautions in Britain and Germany has received little scholarly attention since the end of the Second World War. Of the protective measures brought about as a result of the invention of the bomber, the blackout was by far the most intrusive and extensive form of civil defence. Yet the historiography of the home front and the bombing war in Britain and Germany has tended to sideline the blackout, or else ignore it entirely. The lack of study given to the blackout is at odds with the scale of its impact across wartime society. This thesis furthers understanding of the blackout and the social history of the British and German home fronts by contextualising the blackout within the development of aviation, and its social and economic effects. It also examines the impact technology could have on the relationship between state and citizens, and addresses the lack of comparative research on Britain and Germany during the Second World War. The thesis draws on extensive research conducted in local and national government archives in Britain and Germany, as well as a wide range of secondary literature on the war and inter-war period. It argues that the blackout was a profound expansion of the state into the lives of each nation’s citizens, and though it was set within two politically very different states, it brought with it similar practical and social problems. The blackout, as the most ‘social’ form of civil defence, is an ideal aspect of the war by which to compare the British and German home fronts. Ultimately, the differences between the two countries were less important than the shared sense of obligation that the blackout principle was intended to foster within the wartime community.