Ketamine has demonstrated at a lower dose a robust and rapid antidepressant effect due to a mechanism of action different from conventional treatments. It is now included in several international recommendations on treatment-resistant depression. Ketamine may be used in both out- or in-patient settings, generally by way of intravenous or intranasal formulations provided the fulfillment of safety requirements. There is a growing interest in the use of ketamine for other resistant psychiatric disorders such as anxiety and substance use disorders. Ketamine proves an innovating and promising treatment that extends the range of therapeutic possibilities in psychiatry. We propose here to review its current clinical use.