In response to this growth of the state's correctional populations, and to ensure that sentencing policy is effective and efficient, Illinois created the Sentencing Policy Advisory Council (SPAC) and passed the Crime Reduction Act of 2009. Through its enabling legislation, SPAC is mandated to conduct research and analysis regarding sentencing policy and practices in Illinois, and to examine how these impact correctional populations in the state. The purpose of this briefing is to provide an overview of the sentenced populations and the forces that influence the size and type of the sentenced population, how criminal justice practices have changed in Illinois over the past 20 years, with a specific emphasis on changes in sentencing practices.