Questions concerning the nature of insight in patients with mental illness have interested clinicians for a long time. To what extent can patients understand disorders which affect their mental function? Does insight carry a prognostic value? Is impaired insight determined by the illness or are other factors important? Despite considerable research examining insight in patients with psychoses, non-psychotic disorders and chronic organic brain syndromes, results are inconclusive and insight remains a source of some mystification. Ivana S. Markova examines the problems involved in studying insight in patients with mental illness in order to provide a clearer understanding of the factors that determine its clinical manifestation. She puts forward a new model to illustrate the relationship between different components of insight in theoretical and clinical terms, and points to directions for future research.