Bioscientific concepts of human diversity and politics of inequality have long been intertwined in efforts to order and classify people. The contributors to this volume critically examine the particular ways in which these concepts are constituted and applied across various national contexts and within different life science disciplines, including genetics, medicine, forensics, anthropology, epidemiology, and microbiome research. By highlighting cases outside the dominant research focus on the United States, the authors unpack the epistemological foundations, inherent ambiguities, and political dimensions underlying key classifications—such as race, ethnicity, ancestry, and migration background.