In this Research Paper, ICCT – The Hague Research Fellow Tinka Veldhuis makes an argument for a Realist approach to rehabilitation and reintegration programmes for inmates with a terrorist or extremist background. Accordingly, within the Realist framework, it is stressed that the outcomes of rehabilitation programmes should be understood as a product of the policy mechanisms and the context in which they are implemented. To maximise the likelihood of success it is important to make explicit the underlying assumptions about how the intervention should, given the unique context, contribute to achieving its objectives. This paper endeavours to highlight some of the key questions that need to be answered before and during the implementation of rehabilitation policies.