Teenagers are involved in millions of incidents of “ordinary” aggression each year (U.S. Department of Health and Human Services, 2001). Hundreds of thousands commit serious acts of violence. More than a hundred thousand are arrested for assault. More than one thousand commit lethal assaults. A handful engaged in “rampage shootings,” most infamously the Columbine School Shooting of April 1999, committed by Eric Harris and Dylan Klebold. How are the various points along this continuum of violence (from small aggressions to mass shootings) related to each other? What are the developmental and social foundations for this continuum of violence? These are questions with which this chapter will wrestle.