There is an enormous initiative to establish the genetic basis for disorders of brain function. Unfortunately, genetic intervention is not accomplished easily in the nervous system. One strategy is to engineer and deliver to neurons specialized viral vectors that carry a gene (or genes) of interest, thereby exploiting the natural ability of viruses to insert genetic material into cells. When delivered to brain cells, these vectors cause infected cells to increase the expression of the genes of interest. The ability to deliver genes into neurons in vitro and in vivo with herpes simplex virus (HSV) amplicon vectors has made it possible to carry out exactly these sorts of experiments. This technology has the potential to offer new insights into the etiology of a wide variety of neuropsychiatric disorders. We describe the use of HSV amplicon vectors to study Alzheimer disease, drug addiction, and depression, and discuss the considerations that enter into the use of these vectors both in vitro and in vivo. The HSV amplicon virus is a user-friendly vector for the delivery of genes into neurons that has come of age for the study of brain function.