In 2003, the prison population in England and Wales topped 74,000 for the first time, an increase of more than 60 percent since 1991. This unprecedented rate of increase occurred during a time of gradual decline in the crime rate since the mid-1990's. This study examined why the prison population in England and Wales has increased so significantly at a time when crime rates and court workloads have been dropping. The main elements of the study include: (1) an analysis of Home Office sentencing statistics; (2) focus groups with magistrates, supplemented by questionnaires distributed to participants; and (3) semi-structured interviews with senior judges, Crown Court judges, recorders, and district judges. The first part of the article examines statistics on crime and sentencing to provide an explanation for the rise in the prison population, suggesting that the rise has nothing to do with crime trends or with court workloads but with increased use of imprisonment. The article then examines what factors underlie sentencers’ greater use of imprisonment, and when they do so, to pass longer sentences. The main factors presented behind sentencers greater use of imprisonment include: a more punitive climate of opinion; a more punitive legislative framework; guideline judgments and sentencing guidelines that counteract leniency; some changes in patterns of offending; and senterncers’ perceptions of changes in patterns of offending. The analysis suggests that policies to contain the prison population should involve three levels of intervention: (1) adjustment to the legal and legislative framework of sentencing; (2) softening of the climate of political and public opinion on crime and punishment; and (3) improving understanding of the range of non-custodial penalities. References