This is a comprehensive new history of the French army's critical contribution to the Great War. Ranging across all fronts, Elizabeth Greenhalgh examines the French army's achievements and failures and sets these in the context of the difficulties of coalition warfare and the relative strengths and weaknesses of the enemy forces it faced. Drawing from new archival sources, she reveals the challenges of dealing with and replenishing a mass conscript army in the face of slaughter on an unprecedented scale, and shows how, through trials and defeats, French generals and their troops learned to adapt and develop techniques which eventually led to victory. In a unique account of the largest Allied army on the Western Front, she revises our understanding not only of wartime strategy and combat, but also of other crucial aspects of France's war, from mutinies and mail censorship to medical services, railways and weapons development.