Prison life in Ireland is not exempt from crime. While the common belief holds that a person receiving a custodial sentence will be stripped of opportunities to commit crime, research has shown that this is not always the case. Although little is known about the prevalence of crime in Irish prisons, violence against inmates and staff, criminal damage and drug abuse are not infrequent occurrences, with implications for prison security and overall safety, in addition to rehabilitation efforts. Such crimes present a considerable challenge for fulfilment of the mission of the Irish Prison Service – to provide “safe and secure custody, dignity of care and rehabilitation to prisoners for safer communities.” Understanding why crime in prison takes place requires an understanding of the vulnerabilities that exist within the prison environment, and within the prison population. Problems prior to entering prison – such as mental illness, substance misuse, homelessness, poverty and unemployment, chaotic family backgrounds and social marginalisation – can amplify these vulnerabilities, presenting challenges for the time spent in prison.