Files: WWIpap4.doc; WWI.xls This paper examines the economic aspects of the British mobilisation for World War I and the implications for the state and business. We focus on the following issues: (1) The scale of mobilisation, paying particular attention to the share of GDP devoted to the war effort and the extent of mobilisation in different parts of the economy (2) The way that the mobilisation was financed, examining fiscal and monetary policy (3) The impact of the war on the external account, paying particular attention to the ability of the government to lend abroad to Allies (4) The relative efficacy of government controls and market forces in bringing about the mobilisation of resources (5) The long run impact of the war on wealth, using a national balance sheet approach. In addition to forming a basis for the international comparison of the major combatant countries during World War I, this paper also provides the material for a contrast between the British war efforts during the two World Wars, since the framework draws heavily on our earlier study of World War II.