Criminal behavior and criminal justice decisionmaking are now regarded as complex phenomena involving chance or transient factors as well as discretion. The use of prediction techniques in targeting offenders for investigation, prosecution, bail, and sentencing appears to offer the potential for increasing security by imposing a rational order on the current pattern of discretionary decisionmaking. However, relying on predictive tests creates the potential for penalizing people falsely predicted to commit future crimes. To retributionists, it also seems wrong to assign penalties on the basis of predicted further acts. Others argue that it would be wrong to use factors not under the criminal's control. Predictive tests should be based mainly on prior criminal conduct and used to identify a small and distinctive element of the offending population. Only repeated prior adult convictions should be the basis for predictions of dangerousness. Additional recommendations and 107 references.