The history of intellectual and developmental disabilities (IDD) in the United States is, in many ways, a triumphant story reflecting an increasingly progressive attitude acknowledging the equality of all persons. The law now recognizes people with IDD as citizens, possessing an equal right to education, health care, and employment--each of which represents milestone victories. However, this progression was not a linear development but rather a product of periods of growth and decline, backsliding, and hard-won battles across political, cultural, and legal domains. This article explores the vacillating historical trajectory for people with IDD in the United States from the colonial period to the present. Particular attention is paid to the conceptual understanding of disability itself across time periods as that which informs particular developments in treatment, law, and social status. The capabilities approach, as outlined by Martha Nussbaum, is then brought to bear as a heuristic framework, consonant with current developments in disability studies, and which may guide future social and legislative action.