Only a decade ago, most neuroscientists thought that neurogenesis (the production of new nerve cells) in human beings ended with adulthood. Now, however, it is clear that neurogenesis continues throughout life and may play an important role in adult brain function—including, as the authors propose, in the etiology of depression. Citing evidence that stress reduces neurogenesis and that the most effective antidepressive medications increase it, the authors suggest that the waning and waxing of neurogenesis in the hippocampus might trigger the precipitation of and recovery from episodes of clinical depression.