Pharmacotherapy is not effective for some patients, and there is a need for alternative therapies. In contrast to pharmacological treatments, therapeutic brain stimulation involves the electrical modulation of brain function. Electroconvulsive therapy (ECT) is one example; vagus nerve stimulation (VNS) is another type. The U.S. Food and Drug Administration approved the use of VNS for refractory epilepsy in 1997 and for refractory depression in 2005. In this article, I describe the concept of VNS. Next month’s article will review the clinical studies of VNS for depression and other neuropsychiatric disorders.