How data gathered from national conscriptions in pre-World War I Europe influenced understandings of population fitness and redefined society as a collective body.In pre-World War I Europe, individual fitness was increasingly related to building and preserving collective society. Army recruitment offered the most important opportunity to screen male citizens' fitness, raising questions of how to define fitness for soldiers and how to translate this criteria outside the military context. In this book, Heinrich Hartmann explores the historical circumstances that shaped collective understandings of fitness in Europe before World War I and how these were intertwined with a fear of demographic decline and degeneration. This dynamic gained momentum through the circulation of knowledge among European nations, but also through the scenarios of military confrontations. Hartmann provides a science history of military statistics in Germany, France, and Switzerland in the decades preceding World War I, considering how information gathered during national conscriptions generated data about the health and fitness of the population. Defined by masculine concepts, conscription examinations went far beyond the individuals they tested and measured. Scholars of the time aspired to pin down the "nation" in concrete numerical terms, drawing on data from examinations to redefine society as a "collective body" that could be counted, measured, and examined. The Body Populace explores the historical specificity and contingency of data-gathering techniques, recounts their uses and abuses, and provides a timely contribution to the growing historiography of Big Data. It sheds light on a crucial moment in nineteenth and early twentieth century European history-when statistical data and demographical knowledge shaped new notions of masculinity, fostered fears of degeneration, and gave rise to eugenic thinking.