OVER the last decade, a remarkable change has occurred in the U.S. criminal justice system. Traditionally devoted to the punishment of past crime, it has begun to focus as well on the prevention of future crime by incarceration and control of dangerous offenders. Habitual offender statutes, like “three strikes” laws, sentence repeat offenders to life imprisonment. Jurisdictional reforms lower the age at which juveniles may be tried as adults, increasing the available terms of imprisonment beyond those of juvenile court. Gang membership and recruitment are criminalized. “Megan’s Law” statutes require community notification of a convicted sex offender. “Sexual predator” statutes provide for civil detention of offenders who remain dangerous at the conclusion of their criminal term. Sentencing guidelines increase the sentence of offenders who have a prior criminal history, since these offenders are seen as the most likely to commit future crimes.