Scientific concepts and segregational politics have long been mixed together in attempts to ordering and classifying people by those in power. The contributors to this volume critically examine bioscientific concepts of human diversity as they are applied across various national contexts and within different life science disciplines, including genetics, medicine, forensics, anthropology, epidemiology, and microbiome research. They unpack the epistemologies, ambiguities, and politics of key classifications such as race, ethnicity, ancestry, and migration background. This results in a multidisciplinary analysis of the complex implications of efforts to capture and categorize biological human variation.