Based on a survey of prison policies in 15 countries, the report offers the most comprehensive study to date of the role prisons can play in radicalising people and in reforming them. The report identifies trade-offs and dilemmas but also principles and best practices that will help governments and policymakers spot new ideas and avoid costly and counterproductive mistakes. Among the key findings and recommendations are: The current emphasis on security and containment leads to missed opportunities to promote reform. Prison services should be more ambitious in promoting positive influences inside prison, and develop more innovative approaches to facilitate extremists transition back into mainstream society. Over-crowding and under-staffing amplify the conditions that lend themselves to radicalisation. Badly run prisons make the detection of radicalisation difficult, and they also create the physical and ideological space in which extremist recruiters can operate at free will. Religious conversion is not the same as radicalisation. Good counter-radicalisation policies whether in or outside prison never fail to distinguish between legitimate expression of faith and extremist ideologies. Prison services should invest more in staff training, and consider sharing specialised resources. Individual de-radicalisation and disengagement programmes such as the ones in Saudi-Arabia, Singapore, Indonesia, and other countries can make a difference.