This paper aims to introduce the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) and to set the scene for the forthcoming revision process. The consequences of diseases and disorders at the level of the body (impairment), the person (disability), and the person as a social being (handicap) are defined and described. Bearing in mind some of the controversies and confusions which have become apparent in attempts to apply the ICIDH since its publication in 1980, the distinctions between the different concepts are explored: namely, impairment--disability; impairment--functional limitation--disability; and between disability--handicap. The nature of the classification schemes for these concepts is described, together with some implications for methods of assessment. Finally, the contribution the ICIDH has made, and its potential uses are briefly reviewed.