Most people have a clear sense of what they mean by disability, and have little trouble identifying conditions they consider disabling. Yet providing a clear and consistent definition of disability is far from straightforward. Standardly, disability is understood as the restriction in our abilities to perform tasks, as a result of an impairment of normal physical or cognitive human functioning. However, which inabilities matter? We are all restricted by our bodies, and are all incapable of performing some tasks, but most of these inabilities are not considered disabilities. If, then, we are to avoid the category of disability becoming overly broad—and thus politically and practically useless—we need some way of picking out the specific inabilities that are disabling. I argue that our answer should be informed by an account of the opportunities individuals are entitled to be able to perform as a matter of justice. Thus, to be disabled is to have these opportunities restricted, and not to deviate from the species norm or lack any ability that might improve our well-being.