Participation in crime reflects the distinction between those who engage in crime and those who do not. Frequency of offending is the rate of criminal activity for active offenders. The seriousness of criminal acts and criminal career length suggest different crime control policy options, such as attempts to modify criminal careers. Conceptually, criminal careers may be modified through deterrence, rehabilitation, treatment, or incapacitation. Collective or selective incapacitation strategies may hold the most promise. Incapacitation is based on two key assumptions: (1) criminal activity is patterned with respect to behavior types; and (2) seriousness and rate of offending change in meaningful ways throughout the criminal career. To evaluate the predictability of criminal behavior, a sample of over 6,000 men incarcerated in California prisons in the early 1960's were studied. Data were collected from life histories, official institutional records, questionnaire responses, and psychological testing; 3,108 persons were in the initial study sample, and 3,202 were in the validation sample. Data were also obtained for a sample of men incarcerated in 1980 who were followed through 1988; information was available for 157,936 persons. The men committed over 30,000 crimes since their release from the 1962 incarceration period. Offenses included parole and probation violations, drunken driving, possession or use of drugs, disorderly conduct, gambling, property crimes, and fraud. While nuisance offenses dominated the men's criminal behavior, study participants were also charged with a large number of serious crimes. About one-third of the men were not reincarcerated, but two-thirds spent additional time in prison or jail; nearly one in five was reincarcerated at least six times. For the 1980 sample, the mean number of arrests was 4.83; the men were responsible for 1,976 homicides, 3,371 rapes, 70,639 assaults, 44,885 burglaries, 15,406 robberies, and 84,643 thefts. Incapacitation strategies for all men depended strongly on the concept of patterned criminal activity. For example, when offenders were grouped in terms of the mix of offenses they committed subsequent to release from incarceration, almost 28 percent were charged with only one offense type. Two-offense mixes, however, were relatively common, such as nuisance and property offending. The effectiveness of incapacitation as a form of punishment for career criminals is discussed in terms of criminality prediction. 37 notes, 3 tables, and 14 figures