Sentencing reform since the early 1980s has been dominated by the use of mandatory penalties, determinate sentences, and guideline-based sentences. Of these reforms, mandatory prison sentences have been the most popular. These have been aimed at persons who commit violent crimes, use weapons in the commission of their crimes, are repeat or habitual offenders, or are high- profile drug traffickers. With the implementation of the reforms, there was unprecedented growth in Federal and State prison populations. Now that these sentencing reforms have been in place for more than 15 years, it is clear that the beliefs on which public support rested were largely false. Punishment for serious and violent offenders prior to the reforms was not as lenient as was popularly believed, nor less severe than punishment imposed in other industrialized nations for comparable crimes. The misperception of leniency rested largely on erroneous or badly used data and on the media's attention to unusual or atypically short sentences for violent offenders. In the implementation of the reforms, the definition of a "dangerous" offender was greatly expanded to include nonviolent offenders, notably lower-level drug offenders. There is mixed evidence that these reforms have led to crime reductions. Although violent crimes such as murder have decreased recently, imprisonment is but one of the many reasons. Stabilization of drug markets, community policing efforts, and aggressive enforcement of threatening behaviors have also contributed to the declines in violent crimes. For drug crimes, however, there is no evidence that the increased use of imprisonment has produced measurable reductions. Imprisonment for drug crimes is not a cost-effective sanction compared to treatment or intermediate sanctions, and its overuse for lower level drug offenders is a misallocation of scarce prison resources. Furthermore, the massive increases in incarceration have disproportionately impacted young African-American men in inner-city communities. Within many urban areas, almost 4 percent of African-American men between the ages of 16 and 34 were imprisoned in a single year; this rate exceeded that of comparably aged white men by 7 to 10 times. This has disrupted families and social organization in inner-city communities, thereby contributing to crime problems. 5 tables, 2 figures, and 44 references