The last decade has seen the centrality of the prison within Western systems of criminal justice confirmed. Despite arguments raised in favour of decarceration and alternatives to custody, prison populations in Western Europe and North America have generally continued to rise. The increased reliance on imprisonment has been demonstrated both by new programmes of prison building and by political commitment to the prison, particularly in the UK and USA. Yet imprisonment as a sanction remains contested. A number of differing and conflicting arguments in favour of imprisonment have been used, including rehabilitation, deterrence, incapacitation and justice. In this critical evaluation Thomas Mathiesen examines these arguments and assesses the evidence for and against their viability as justifications for the prison. In each case the author finds the arguments supporting the effectiveness of the prison as a punishment seriously wanting. From this analysis of the rationale for the prison the author moves on to the question of political actions. If imprisonment is ultimately indefensible, how can a significant reduction in the in-prison population be obtained, what can be done about offenders and what can be done for victims? Looking again at the bases for criminal justice and social policy, Thomas Mathiesen's arguments will be of interest to criminologists and others involved in the study and practice of the criminal justice system. Thomas Mathiesen has also written "The Defences of the Weak", "The Politics of Abolition" and "Law, Society and Political Action".