Ten years after the school massacre in Columbine, Colorado, school shootings are a new and alarming epidemic. While sociologists have attributed the trigger of violence to peer pressure, such as bullying and social isolation, prominent psychologist Peter Langman, argues here that psychological causes are responsible. Drawing on 20 years of clinical experience, Langman offers surprising reasons for why some teens become violent. Langman divides shooters into four categories, and he discusses the role of gender, trauma, paranoia, and other disturbances, as factors that activate psychotic tendencies. From examining the material evidence of notorious school shooters at Columbine and Virginia Tech to addressing the mental states of the violent youths he treats, Langman shows how to identify early signs of homicide-prone youth and what preventive measures parents and communities can take to protect themselves from the tragedy.