When is neurodegeneration a disease? What is brain health in an aging society? Different disciplines have discussed these and other questions about Alzheimer’s disease. This chapter deals with the philosophical implications of questioning Alzheimer’s disease and is structured along three parts. First, we sketch out the past and present plurality of approaches to the contested status of various forms and conceptualizations of “Alzheimer’s” as a societal phenomenon, “Alzheimer’s disease” as a clinical diagnosis, and “AD” as a biomedical object. Second, we argue that the three most prevailing scientific approaches—targeted toward biomarkers, treatments, and prevention—share an epistemological underdetermination with respect to the relationship between the evidence and the validity of each approach. Finally, we argue that this underdetermination is evidenced in scientific disagreements about how to prioritize the different parts and interlacements of societal phenomena (“Alzheimer’s”), clinical diagnoses (“Alzheimer’s disease”), and biomedical objects (“AD”). We highlight the growing demand for engagement with the methodological details and social epistemology of the Alzheimer’s research field and for a more scientifically embedded philosophical reflection and intervention. We conclude that within philosophy of medicine, the unstable category of Alzheimer’s disease is an opportunity for reflection on the aims and scope of biomedicine and philosophy of medicine alike.