Remission, i.e. the complete absence of symptoms, is the major goal in the treatment of major depressive disorders because residual symptoms cause less functioning and a worse outcome. Despite several treatment steps, numerous patients do not reach complete remission of symptoms. In these patients, it is necessary to rule out several possible causes, including inadequate pharmacotherapy, to confirm the diagnosis of treatment-resistant depression (TRD). In the treatment of TRD, pharmacotherapy plays a central role. Nonpharmacological treatment strategies such as psychotherapy, electroconvulsive therapy, and other brain stimulation methods are also used for TRD treatment and are discussed elsewhere in this issue. Regarding complex pharmacotherapy of TRD, only a limited number of randomized-controlled trials have been done. In consequence, treatment decisions are often based on clinical experience, case series, and uncontrolled studies. Nevertheless, there are some interesting new developments, which are summarized and assessed on the basis of existing evidence in this article. Afore, we present an overview of the most important definitions, epidemiologic data, diagnostic needs and methods for treatment optimization. We end with a critical view on the present and future development of antidepressant drugs.