Common sense regards disability as a simple natural fact, but the sociology of disability emphasizes that disability has to be differentiated from impairment. Not every chronic health condition is acknowledged as a disability. There are cultures in which the social fact of disability does not exist. Disability as a social problem has evolved as a product of the modern welfare state. With the beginning of modernity and, above all, during the period of industrialization, a line was drawn between “the disabled” and other poor and unemployed people. In the course of the twentieth century, disability became a horizontal category of social stratification. Even today the ascription process is ambivalent, for it includes rights and benefits as well as discrimination and segregation. A recent development in the sociology of disability is to discuss disability in relation to citizenship and human rights.