Non-depressed lay persons have been shown to have extensive and accurate knowledge about depression (Rippere, 1977, 1980 a, b, 1981 a) that is underpinned by a structure that resembles current academic theories of the disorder (Furnham & Kuyken, 1991). In this study a semi-structured interview schedule and a number of rating scales were used to determine and compare the nature and extent of depressed patients', clinical psychologists', and lay persons' beliefs about the causes of depression. We confirmed that depressed patients and non-depressed lay persons alike have relatively extensive beliefs about the causes of depression which are comparable to those held by clinical psychologists. However, depressed patients tend to endorse biological explanations of the causes of depression to a greater extent than clinical psychologists. In contrast, clinical psychologists assign a more important causal role to unconscious processes and childhood vulnerability factors than do either depressed patients or non-depressed lay controls.