It reveals that the increases in the numbers of felony drug arrests, drug convictions, and the defendants with prior felony convictions changed the number and nature of felony offenders sentenced. These changes accounted for almost all of the increases in prison populations. The number of felony drug arrests more than tripled from 13,901 in 1981 to 50,645 in 1989, an increase far greater than for violent felonies or other types of felonies. In addition, prosecutors became increasingly efficient at obtaining felony convictions for drug offenders. Nevertheless, the seriousness of arrest charges did not change from 1981 to 1989, and judges did not change their rate of incarcerative sentences for comparatively situated offenders. The increase in the number of drug offenders with prior felony convictions radically changed the impact of predicate offender laws on incarceration, although it is questionable whether the framers of the 1973 predicate offender laws intended to focus so much prison resources on nonviolent offenders. Tables, figures, and 10 references (Author summary modified)