For almost the first time working with ISRD data, this chapter explores the seriousness of criminal victimization and offending. Seriousness is examined first as an attribute of individuals, looking at repeat victims and repeat offenders, and second as an attribute of incidents, looking at those which involve greater harm. Focusing on individuals shows that most victims were repeat victims, and most offenders were repeat offenders. Analysis of the prevalence and incidence of repeat victimization and offending showed mixed results in terms of gender and age, while the measures of variety revealed generalized rather than specialized offending (and victimization). Focusing on incidents of assault (victimization) and weapon carrying (offending) shows a consistent link between their overall prevalence and the prevalence of their more serious forms as identified in this chapter. Additionally, different measures of seriousness were consistently related to one another. In relation to cross-national patterns, the prevalence of repeat victimization tended to be higher in countries with a lower human development index (IHDI), but the incidence of repeat victimization and offending was higher in countries with a higher IHDI. However, no clear cross-national patterns were found in relation to the characteristics of serious incidents.