In early November 1914 the German military authorities ordered the internment of all British male civilians aged between 17 and 55 then still resident in Germany. Over four thousand British subjects were affected by this measure. This article examines the domestic political background to the decision in favour of internment, focusing on the role of public opinion and of competing voices within the German war leadership. It also looks at attempts to negotiate the release and exchange of civilian prisoners after 1914. Internment was supported by the military and by most sections of the middle-class press. While partly a reaction to similar measures against Germans in Britain, it also reflected the government's growing frustration at the failure to achieve victory in the opening months of the war.