Although the concept of partial or incomplete remission from depression has been noted in the literature for many decades, it is only recently that a precise definition of partial remission has been formulated (1). This paper reviews publications relating to this concept, in terms of prevalence, clinical characteristics and implications for prognosis. There have been too few studies to allow conclusive evidence to be presented, but partial remission may affect one third of subjects treated for depression, and may increase the risk of further depressive relapse and adversely affect social and work performance. This paper highlights the need to increase awareness of this concept among clinicians so that residual symptoms may be aggressively treated, and also comments on the need for researchers to consider this important group in all treatment and outcome studies.