Building on prior conceptual schemes, this article presents a sociomedical model of disability, called The Disablement Process, that is especially useful for epidemiological and clinical research. The Disablement Process: (1) describes how chronic and acute conditions affect functioning in specific body systems, generic physical and mental actions, and activities of daily life, and (2) describes the personal and environmental factors that speed or slow disablement, namely, risk factors, interventions, and exacerbators. A main pathway that links Pathology, Impairments, Functional Limitations, and Disability is explicated. Disability is defined as difficulty doing activities in any domain of life (from hygiene to hobbies, errands to sleep) due to a health or physical problem. Feedback effects are included in the model to cover dysfunction spirals (pernicious loops of dysfunction) and secondary conditions (new pathology launched by a given disablement process). We distinguish intrinsic disability (without personal or equipment assistance) and actual disability (with such assistance), noting the scientific and political importance of measuring both. Disability is not a personal characteristic, but is instead a gap between personal capability and environmental demand. Survey researchers and clinicians tend to focus on personal capability, overlooking the efforts people commonly make to reduce demand by activity accommodations, environmental modifications, psychological coping, and external supports. We compare the disablement experiences of people who acquire chronic conditions early in life (lifelong disability) and those who acquire them in mid or late life (late-life disability). The Disablement Process can help inform research (the epidemiology of disability) and public health (prevention of disability) activities.