In the eighteenth century, as wars between Britain, France, and their allies raged across the world, hundreds of thousands of people were captured, detained, or exchanged. They were shipped across oceans, marched across continents, or held in an indeterminate limbo. The Society of Prisoners challenges us to rethink the paradoxes of the prisoner of war, defined at once as an enemy and as a fellow human being whose life must be spared. Amidst the emergence of new codifications of international law, the practical distinctions between a prisoner of war, a hostage, a criminal, and a slave were not always clear-cut. Renaud Morieux's vivid and lucid account uses war captivity as a point of departure, investigating how the state transformed itself at war, and how whole societies experienced international conflicts. The detention of foreigners on home soil created the conditions for multifaceted exchanges with the host populations, involving prison guards, priests, pedlars, and philanthropists. Thus, while the imprisonment of enemies signals the extension of Anglo-French rivalry throughout the world, the mass incarceration of foreign soldiers and sailors also illustrates the persistence of non-conflictual relations amidst war. Taking the reader beyond Britain and France, as far as the West Indies and St Helena, this story resonates in our own time, questioning the dividing line between war and peace, and forcing us to confront the untenable situations in which the status of the enemy is left to the whim of the captor.