In this article, we summarize key findings from 20 years of research conducted at the intersection of developmental psychology and juvenile justice in the United States. We predominantly examine data from two large-scale, multisite longitudinal studies involving justice-system-involved adolescents—the Pathways to Desistance study and the Crossroads study. Topics of discussion include predictors of offending and desistance from crime; youth outcomes and psychosocial needs; and emerging research, programs, and policy initiatives. First, individual-level (e.g., age, psychosocial maturity) and contextual-level (e.g., antisocial peers, exposure to violence) risk factors associated with offending are explored. Second, we discuss short-term and long-term outcomes of justice-system contact for youths engaging in moderate offenses. We highlight main findings from the Crossroads study indicating that youths who are sanctioned by the justice system at their first arrest have worse outcomes than youths who are diverted from formal processing. Additionally, we discuss the high prevalence of youths’ exposure to violence and mental health disorders as well as the differential treatment of youths of color in the justice system. Third, we extend the conversation to justice-system-involved young adults and discuss emerging, innovative legal solutions, including young adult courts. Last, we discuss real-world implications of these findings.