There has been a growing trend in recent years towards the adoption of evidence-based policy in a variety of fields, including criminal justice. The purpose of evidence-based policy is to guide the activities of organisations based on scientifically verified facts, enabling the development of effective and efficient policies. In this article, we introduce the commitment of the Israel Prison Service (IPS) to the implementation of evidence-based policy by detailing the processes and development of a large-scale research programme in the IPS. We illustrate how the cooperation and commitment of key individuals, including successive IPS Commissioners, have enabled the implementation of evidence-based policy in a hierarchal organisation. Within this context, we demonstrate how human agency is a key factor in the successful implementation of the policy in criminal justice settings. By following the different stages of development and implementation, the example of the IPS also highlights the importance of agencies taking ownership of science. We conclude by arguing that the road to evidence-based policy is a ‘winding road’, highlighting the key turning points that influenced the institutionalisation of the policy in the IPS.