The justification is based on two considerations. First, a candid, public consideration of offender 'dangerousness' is preferable to the arbitrary and unarticulated assumption upon which current sentencing rests. Second, and a more selective determination of who should occupy available prison space can remedy the current prison population crisis. 'Selective incapacitation' is defined, and obstacles facing policymakers who promote selective sentencing are identified. The need to determine which crimes should provoke consideration of longer sentences is noted, and a review of prior violent criminal activity is suggested. Federal proposals, it is emphesized, limit the application of selective incapacitation to offenders with prior violent criminal activity. The reliance solely on previous convictions raises problems, however, because convictions notoriously underrepresent the volume of reported crime. Reliance on past arrests, particularly juvenile arrests for violent crime, is recommended. Moreover, a policymaker must determine what offender variables, if any, should be used in constructing a selective incapacitation policy, and also determine which offenders should be subjected to such a policy. Bail and parole release are discussed as practices that may promote injustice, and benefits of selective incapacitation are examined. Finally, the paper concludes that properly implemented policy of selective incapacitation is an important part of criminal justice reform strategy. Included are 35 references.