Resulting challenges for prison managers include questions about excessive reliance on imprisonment as punishment, racial disparity, the appropriateness of the inmates for whom imprisonment is imposed, problems of crowding and program access, the effectiveness of imprisonment, and the cost of imprisonment. Complicating the management task is the need to grapple with emerging health care problems such as HIV and tuberculosis, the importance of rapidly recruiting and training staff, and planning for the effects of a dynamic legislative environment with the passage of new laws such as "three strikes" and with the elimination of traditional behavioral incentives such as earned "good time." Trends in the use of imprisonment are reviewed, with emphasis on average sentence length and time served, the impact of increasing arrests and higher probabilities of incarceration, changing Federal sentencing linked to population growth, and the increase in the number of violent and drug offenders. The authors point out that sentencing policies introduced in recent years have substantially altered the procedures used to determine time served and release eligibility and that these changes will most directly affect criminals with the longest time to serve. 20 references, 2 tables, and 4 figures