 “Disability” is typically defined in terms of two elements: (i) a physical or mental characteristic labeled or perceived as an impairment or dysfunction, and (ii) a significant personal or social limitation associated with that characteristic. The relationship between these two elements—and the role of the environment in mediating them—is a core issue in the conceptualization of, and social response to, disability. The medical model treats disability as an individual physical or mental characteristic with significant personal and social consequences. In particular, it sees the limitations faced by people with disabilities as resulting primarily or solely from their impairments. By contrast, the various social models see disability as a relationship between individuals and their social environments: physical and mental characteristics are limiting only or primarily in virtue of social practices that lead to the exclusion of people with those characteristics. This exclusion is manifested not only in deliberate segregation, but in built environments and social practices that restrict the participation of people regarded as having disabilities (see SEP entry on  disability: definitions, models, experience).