The International Classification of Functioning, Disability and Health (ICF; World Health Organization [WHO], 2001), and its predecessors the International Classification of Impairments, Disabilities and Handicaps (ICIDH and ICIDH - 2; WHO, 1980, 1999) have been influential in the conceptualization of the construct of disability in the United States and internationally for more than three decades. This chapter begins with a brief overview of the history of classification of health and illness, and the role that different conceptualizations of disability have played along the way. It then reviews the development of the ICF within the context of these conceptualizations and introduces its key concepts, conceptual framework, and a brief orientation to its use. It concludes with consideration of the current and future impact of the ICF on conceptualizing psychological and social aspects of illness and disability.