The study examined official record data available to prosecutors in the two jurisdictions to learn which items of information most accurately identified offenders as high-rate (committing crimes frequently) and dangerous (committing violent crimes). Although much of the information usually available to prosecutors was found useful for identifying high-rate, dangerous offenders, the study found that other commonly used information can be misleading or ineffective for purposes of identification. The study found that prosecutors evaluate separately the three dimensions of a defendant's criminality: rates of committing crimes, dangerousness, and persistence. Defendants who were identified as high-rate and dangerous by prosecutors in one site were also identified as high-rate and dangerous by prosecutors in the second site. Written office guidelines regarding selection criteria for career criminals promote consistency in deputy district attorneys' judgments about the kinds of defendants who are high-rate, dangerous offenders. Long-term persistent offenders may or may not be high-rate, dangerous offenders; habitual criminality should not be confused with high-rate, dangerous criminality. Although some existing guidelines for identifying high-rate, dangerous offenders are valid and useful, greater accuracy may be obtained through a two-stage screening process. Once a group of high-rate offenders was identified, the subset of high-rate, dangerous offenders could be identified by using a small number of criteria that include elements of the instant crime. Several factors proven not to be indicative of high-rate, dangerousness were the display or use of a gun to threaten a victim; alcoholism; number of prior arrests for drug distribution or possession; number of adult convictions for assault, burglary, auto theft, robbery, or receipt of stolen property; record of previous probation or parole revocations; and a record of previous incarceration. The study also found that the most criminally active defendants in one jurisdiction (Middlesex County, Mass.) and the most criminally active defendants in the second jurisdiction (Los Angeles County) committed crimes at essentially the same rates. 13 notes, questions for discussion, and suggested student applications of the chapter material