Neurosteroids are steroids that rapidly alter neuronal excitability by interacting with cell surface receptors, mainly the GABA/A receptor complex. Neurosteroids are synthesized both in the central nervous system and in peripheral tissues, from which they enter the brain via systemic blood circulation. Neurosteroids may regulate emotional behavior, and may therefore be important in the development of the depressive disorders: major depression, post-traumatic stress disorder, premenstrual dysphoric disorder, and postpartum depression. Studies of neurosteroids offer potential new treatments of depressive disorders.