Part I sketches the changing conceptions of adolescence that have been reflected in the evolution of juvenile justice policy over the past century. Part II presents a developmental framework. It first describes the role of antisocial conduct in adolescent development and sketches the taxonomy, which includes two categories of youthful criminal behavior: "adolescent- limited" and "life-course-persistent." It then offers a positive account of developmental factors that may influence decision-making in ways that distinguish adolescents from adults. This framework is then applied in examining the impact of developmental factors on decisions to engage in criminal conduct and on decisions in the criminal process. Part III explores the possible implications of developmental knowledge for criminal blameworthiness, and it concludes that evidence from developmental psychology supports a presumption of youthful diminished responsibility for younger and mid-adolescents. It then examines through a developmental lens the utilitarian argument that societal protection necessitates severe penalties for youthful offenders. This perspective suggests that punitive policies may poorly serve the efficiency goals of their supporters. Part IV examines the lessons of the developmental perspective for juvenile justice policy and suggests some directions for policy that is formulated in a developmental framework. 185 notes