The literature on successful aging reveals a wide range of definitions, generally reflecting the academic discipline of the investigator. Biomedical models primarily emphasise physical and mental functioning as successful aging; socio-psychological models emphasise social functioning, life satisfaction and psychological resources as successful aging. Several studies also identify these factors as the precursors of successful aging. Moreover, research shows that older people consider themselves to have aged successfully, but classifications based on traditional medical models do not. Fewer studies have explored lay views, and most of these have been exploratory or restricted to specific groups of areas. A model of successful aging needs to be multi-dimensional, incorporate a lay perspective for social significance, use a continuum rather than dichotomous cut-offs for "success" and lack of, and distinguish clearly between predictor and constituent variables.