Neuropsychological deficits are a common feature of depressive disorders. In the systems ICD 10 and DSM IV neuropsychological deficits constitute a relevant diagnostic criterion. Deficits in executive functions, attention and memory are documented. Primarily, mental flexibility seems to be impaired. The relation between neuropsychological deficits and depression is moderated by the patient's age. In the elderly, depression is more often accompanied by neuropsychological deficits. Clinically, the relevance of neuropsychological testing in depression has different aspects. Neuropsychological testing is the prerequisite for neuropsychological therapy when patients exhibit residual cognitive symptoms, and for professional and social rehabilitation. The neuropsychological outcome provides important information for the therapy process, and for predicting therapy success. In addition, neuropsychological testing can influence the choice of medication and psychotherapy. Neuropsychological data can also help to differ depression from dementia, an important problem in elder psychiatric and neurological patients. For this purpose a comprehensive neuropsychological test-battery that covers different neuropsychological domains needs to be employed. Furthermore, the analysis of the patients behavior and errors during testing provides essential information. However, in many cases a neuropsychological re-test and the analysis of the course of neuropsychological deficits is needed to differ depression from dementia.