The chapter offers definitions of SVJ offenses in terms of both official records and self-reports, and reviews serious and violent offending in the context of past classification systems. The chapter examines the extent to which SVJ offenders overlap with chronic offenders and whether the overlap is similar to that between serious nonviolent and chronic juvenile offenders. The issue of overlap is important because the juvenile courts seek to punish and discourage those at highest risk of reoffending, to focus scarce resources on the chronically violent offender. The chapter also examines: changes in the prevalence of chronic offending; how knowledge of SVJ offenders depends on the type of data used to examine them; the extent to which chronic juvenile offenders are responsible for the total amount of delinquency committed by juveniles; and whether SVJ offenders are concentrated in particular geographic areas, by geographically plotting homicides committed by juveniles in the United States. Figures, table, note