Truth in sentencing (TIS) refers to a range of sentencing practices that aim to reduce the uncertainty about the length of time that offenders must serve in prison. During the 1990's, throughout the States and in the Federal Government there was considerable legislative activity related to TIS. The first chapter describes the variety of forms of TIS and analyzes the changes in the Federal TIS grant eligibility requirements. This is followed by a chapter that addresses the influence of the Federal TIS grant program on sentencing reform changes in the States. The third chapter presents the results of the empirical analysis of changes in prison population outcomes in relation to changes in sentencing reforms. This analysis was conducted for seven States. The study found that when implemented as part of a larger sentencing reform process, TIS reforms are associated with large changes in prison population outcomes. In States that did not make changes to their sentencing structures by implementing TIS, changes in prison population outcomes were more strongly influenced by changes in pre-sentencing factors than by changes in sentencing practices. In States that made moderate to marginal changes in their sentencing structure when they implemented TIS, the effects of changes in sentencing practices on prison outcome generated two patterns. First, changes in the prison admission rate for violent offenders had a larger influence on prison population outcomes than did changes in expected length of stay. Second, the increase in percentage requirements led to larger increases in length of stay and consequently, a larger effect of length of stay on the expected number of prisoners. Finally, as TIS was implemented during a period when violent crime was decreasing, in some States arrests for violent crimes led to large decreases in the expected number of prisoners and in the number of prison admissions. In States with determinate sentencing and no parole release, the absence of a "release valve" on the correctional system could potentially pose new challenges for managing corrections populations if violent crimes and arrests increase and if sentencing practices under TIS mirror those observed in 1996 or 1998. This result suggests that TIS as a corrections management tool has limited effectiveness. 3 exhibits