The varieties of criminal behavior identified can be approximately ordered according to public perception of the relative seriousness of the offenses they encompass. The variety of criminal behavior an offender reports is strongly correlated with two other measures of seriousness: his annual rate of committing crimes and the persistence of his criminal behavior. The most serious variety comprises the violent predators: offenders who concurrently rob, assault, and deal drugs. The violent predators are characterized by relatively long, violent criminal careers which began as young juveniles; heavy involvement in selling and taking hard drugs; their willingness to commit robbery; and the high rates at which they tend to commit all other income-producing crimes. A moderately good distinction can be made between violent predators and less serious varieties of offenders from detailed information about juvenile behavior, employment, and drug use. Knowledge about high-cost heroin addiction and frequent use of high quantities of nonopiate psychotropic drugs are especially useful for making this distinction. The problems of false identifications and inadequate official records preclude using the identified classifications as the basis for criminal justice decisions about individual offenders, but the findings do have important implications for understanding crime rates and crime-control policies, particularly drug enforcement. The appendixes discuss technical issues related to the research, and tabular data are provided. (Author summary modified)