Throughout its history as a social science, demography has been associated with an exclusively quantitative orientation for studying social problems. As a result, demographers tend to analyse population issues scientifically through sets of fixed social categories that are divorced from dynamic relationships and local contexts and processes. This volume questions these fixed categories in two ways. First, it examines the historical and political circumstances in which such categories had their provenance, and, second, it reassesses their uncritical applications over space and time in a diverse range of empirical case studies, encouraging throughout a constructive interdisciplinary dialogue involving anthropologists, demographers, historians, and sociologists. This volume seeks to examine the political complexities that lie at the heart of population studies by focusing on category formation, category use, and category critique. It shows that this takes the form of a dialectic between the needs for clarity of scientific and administrative analysis and the recalcitrant diversity of the social contexts and human processes that generate population change. The critical reflections of each chapter are enriched by meticulous ethnographic fieldwork and historical research drawn from every continent. This volume, therefore, exemplifies a new methodology for research in population studies, one that does not simply accept and re-use the established categories of population science but seeks critically and reflexively to explore, test, and re-evaluate their meanings in diverse contexts. It shows that for demography to realise its full potential it must urgently re-examine and contextualize the social categories used today in population research.