Treatment-resistant depression (TRD) is a prevalent, disabling, and costly condition affecting 1%–4% of the U.S. population. Current approaches to managing TRD include medication augmentation (with lithium, thyroid hormone, buspirone, atypical antipsychotics, or various antidepressant medications), psychotherapy, and ECT. Advances in understanding the neurobiology of mood regulation and depression have led to a number of new potential approaches to managing TRD, including medications with novel mechanisms of action and focal brain stimulation techniques. This review will define and discuss the epidemiology of TRD, review the current approaches to its management, and then provide an overview of several developing interventions.