Disability is lack of ability relative to a personal or group standard. Disability may involve physical impairment, sensory impairment, cognitive or intellectual impairment, mental disorder (also known as psychiatric disability), or various types of chronic disease. A disability may occur during a person's lifetime or may be present from birth.

Disability may be seen as resulting directly from individuals, in which case the focus is typically on aspects of those individuals and how they could function better. This view is associated with what is generally termed a medical model of disability. Alternatively, the interaction between people and their environment/society may be emphasized. The focus may be on the role of society in labeling some people as having a disability relative to others, while causing or maintaining disability in those people through attitudes and standards of accessibility that favor the majority (a prejudice dubbed "able-ism"). This view is commonly associated with a human rights or social model of disability.

On December 13, 2006, the United Nations formally agreed on the Convention on the Rights of Persons with Disabilities, the first human rights treaty of the 21st century, to protect and enhance the rights and opportunities of the world's estimated 650 million disabled people. Countries that sign up to the convention will be required to adopt national laws, and remove old ones, so that persons with disabilities would, for example, have equal rights to education, employment, and cultural life; the right to own and inherit property; not be discriminated against in marriage, children, etc; not be unwilling subjects in medical experiments.

In 1976, the United Nations launched its International Year for Disabled Persons (1981), later re-named the International Year of Disabled Persons. The UN Decade of Disabled Persons (1983-1993) featured a World Programme of Action Concerning Disabled Persons. In 1979, Frank Bowe was the only person with a disability representing any country in the planning of IYDP-1981. Today, many countries have named representatives who are themselves individuals with disabilities. The decade was closed in an address before the General Assembly by Robert Davila. Both Bowe and Davila are deaf. In 1984, UNESCO accepted sign language for use in education of deaf children and youth.

The disability rights movement

The disability rights movement, led by individuals with disabilities, began in the 1970s. This Self-advocacy is often seen as largely responsible for the shift toward independent living and accessibility. The term "Independent Living" was taken from 1959 California legislation that enabled people who had acquired a disability due to polio to leave hospital wards and move back into the community with the help of cash benefits for the purchase of personal assistance with the activities of daily living.