Where do our conventional understandings of health, illness, and the body stem from? What makes them authoritative? How are the boundaries set around these areas of life unsettled in the changing historical and political contexts of science, technology, and health care delivery? These questions are at the heart of Troubling Natural Categories, a collection of essays honouring the tradition of Margaret Lock, one of the preeminent medical anthropologists of our time. Throughout her career, Lock has investigated how medicine sets boundaries around what is deemed "normal" and "natural, " and how, in turn, these ideas shape our technical and moral understandings of life, sickness, and death. In this book, nine established medical anthropologists - all former students of Lock - critically engage with her work, offering ethnographic and historical analyses that problematize taken-for-granted constructs in health and medicine in a range of global settings. The essays elaborate cutting-edge themes within medical anthropology, including the often disturbing, inherently political nature of biomedicine and biotechnology, the medicalization of mental health processes, and the formation of uniquely "local biologies" through the convergence of bodily experience, scientific discourse, and new technologies of care. Troubling Natural Categories not only affirms Margaret Lock's place at the forefront of scholarship but, with these essays, carves out new intellectual directions in the medical social sciences. Contributors include Sean Brotherton, Vinh-Kim Nguyen, Junko Kitanaka, Stephanie Lloyd, Dominique Behague, and Annette Leibing.