Residual symptoms, despite successful response to therapy, appear to be the rule in unipolar depression. Most of the residual symptoms occur in the prodromal phase of illness. Residual symptoms are associated with biological correlates, mainly involving the hypothalamic-pituitary-adrenal (HPA) axis and the sleep architecture. They are powerful predictors of relapse. These findings have led to the hypothesis that residual symptoms upon recovery may progress to become prodromal symptoms of relapse. A sequential strategy (encompassing pharmacotherapy in the acute phase of illness and cognitive behavioral therapy in its residual phase) has been developed and was found to be effective in decreasing relapse rate in controlled studies. A largely untested assumption in unipolar depression is that pharmacological strategies that are effective in the short term are the most suitable for postacute and residual phases or maintenance. The literature on subclinical symptomatology calls for specific, stage-oriented, therapeutic approaches. The efficacy of antidepressant drugs may be assessed not only on differential remission rates, but also on differential amount of residual symptomatology after response.