The Medical War describes the role of medicine in the British Army during the First World War. Mark Harrison argues that medicine played a vital part in the war, helping to sustain the morale of troops and their families, and reducing the wastage of manpower. Effective medical provisions were vital to the continuation of the war in all the major theatres, for both political and operational reasons.

The Medical War is divided more or less evenly between an analysis of medicine on the Western Front and selected campaigns in other theatres of the war, principally Mesopotamia, Gallipoli, Salonika, East Africa, and the Middle East. It explores preventive medicine and casualty disposal and treatment, attempting to view these not only from the perspective of medical personnel but also from that of commanders, patients, politicians, and the general public. In providing this wide-ranging geographical and thematic coverage of medicine, The Medical War is unique among books on medicine in the First World War. It also differs from existing work in considering the British Army's medical responsibilities for non-British troops and labourers, principally those of the Indian Army and various colonial labour detachments.