Youth crime and other types of risk behavior have declined considerably over the last 20–30 years in many developed countries. Robust evidence comes from both official crime data and repeated self-report surveys, one of them covering 36 countries in Europe over 20 years. Since 2015, the decline appears to have leveled off, with a reversal for property crimes in some European countries. Disaggregated crime trends show some but no unequivocal signs of “polarization” between declining prevalence rates and constant or increasing incidence rates, in particular for violent offenses. They also provide conflicting signs of social or ethnic inequalities in the crime drop. Studies based on repeated cross-sectional surveys from the United States and Scandinavia, looking at microlevel proximal influences, have made progress in finding explanations of the crime drop. These studies find that declines in unstructured socializing with peers and in alcohol consumption are the two strongest predictors of declining rates of offending over time, supporting routine activity approaches. The roles of the internet and social media in social changes of adolescents’ life experiences remain unclear and underexplored.