Most discussions of legal and social policies that justify different penal treatment for violent acts by adolescent offenders ignore basic substantive issues; youth crime policy has been preoccupied with procedural and jurisdictional matters. Justification for separate treatment of juveniles can be found both in the principles of the penal law and in social policies that recognize adolescence as an important learning period. Three dimensions of adolescent diminished responsibility stand out: incomplete comprehension of moral duty, deficient capacity to manage impulses, and vulnerability to peer pressure that is the hallmark of adolescent law violation. Social policy favoring youth development does not require a discounting of penal liability but suggests an effort to avoid using punishments that limit the opportunity of adolescent offenders to survive into normal adulthood. Figure, references