This document serves as a guide to the various definitions of disability used in surveys in order to identify disabled people. The Office for Disability Issues is encouraging the use of a single harmonised definition of disability that reflects the Disability discrimination act and is a minimum standard for public bodies to use as part of their duties under the Disability equality duty. Such a unification of definitions of disability is necessary because it will reduce the influence of methodological differences and provide a clearer view of changes over time in the disabled population and outcomes for disabled people. The Disability discrimination act defines a disabled person as a person with: a physical or mental impairment which has a substantial and long-term adverse effect on his ability to carry out normal day-to-day activities. This guide clarifies this definition, and the terms used by the act, as well as outlining the special provisions and recommending questions to identify people included under this definition.