Adolescence is the developmental transition from childhood to adulthood in which youth undergo substantial biological, cognitive, and psychosocial maturation. This developmental maturation equips youth with the skills and capacities needed in adulthood. However, these developmental processes occur gradually and on different trajectories. Neurological changes intensify adolescents’ emotional reactivity and reward sensitivity – often overpowering less developed cognitive control systems. Additionally, heavy reliance on peer status and affiliation, difficulty considering long-term consequences, and limited life experiences contribute to adolescents’ increased risk taking and potential for contact with the justice system. These types of observable normative adolescent characteristics served as the basis for creating the juvenile justice system – a legal system distinct from the criminal justice system that recognised youths’ immaturity relative to adults, decreased culpability for their actions, and increased amenability to change and rehabilitation. Despite the late twentieth century’s shift toward a more punitive juvenile justice system, advances in neuroscience and behavioural research in the early twenty-first century have contributed to efforts to reform juvenile justice system policies and practices to better reflect youths’ developmental capacities and potential for successful transitions into adulthood. This entry reviews the developmental and neuroscience research, alignment between these research findings and existing juvenile justice policy and practice, and ways in which recent and ongoing reform efforts seek to better align the juvenile justice system with empirical findings on youths’ functioning and decision-making capacities.