Anglo-American relations were transformed during the First World War. Britain was already in long-term economic decline relative to the United States, but this decline was accelerated by the war, which was militarily a victory for Britain, but economically a catastrophe. This book sets out the economic, and in particular, the financial relations between the two powers during the war, setting it in the context of the more familiar political and diplomatic relationship. Particular attention is paid to the British war missions sent out to the USA, which were the agents for much of the financial and economic negotiation, and which are rescued here from underserved historical obscurity.