Is obesity a disease? Much ink has been spilled over this debate and for good reasons. The global prevalence of obesity has more than doubled since the 1980s and is now of pandemic proportions. Whether obesity is a disease has consequences for what kind of treatments are appropriate, as well as how we ought to allocate funding and access to healthcare resources. In most cases, there is no dispute over the medical facts, yet disagreement persists. This is because whether obesity is a disease is not determined by medical facts alone; the issue is, in part, conceptual. Science relies on careful argumentation and conceptual analysis as part of its armamentarium. In this review, we will examine the two concepts of disease most often employed in the philosophy of medicine: the naturalistic and constructivist. We will argue that, whichever definition of a disease is used, obesity fits the criteria for disease definition. Those seeking to meet the challenge of managing obesity will, therefore, need to embrace chronic disease models of care suited to addressing the lifelong challenge posed by this disease and its associated complications.