Drawing on data from the fourth International Self-Report Delinquency Study (ISRD4), this chapter compares adolescents’ experiences of victimization and offending in online and offline contexts across 21 countries. While offline victimization (21.5%) and offending (14.8%) remain more prevalent, online harms are widespread: 18% of respondents suffered at least one online victimization and 7.9% admitted to an online offense in the past year. Gender and age patterns diverge—girls are slightly more vulnerable online, boys dominate offending, and 13–15-year-olds show the highest digital misbehavior. Overlap analyses using Loevinger’s H reveal moderate-to-strong links between online and offline victimization (H = 0.39) and even stronger links for offending (H = 0.48), suggesting common lifestyle and routine-activity risk factors across domains. Substantial cross-national variation emerges, yet aggregate connectivity measures (e.g., ICT Development Index) do not account for these differences. The findings underscore the continuing relevance of traditional criminological patterns, the growing importance of digital settings, and the need for integrated theory and policy that address both spheres.