This article explores the reasons behind government support for the evidence-based approach and considers the limitations of this concept. In the criminal justice field the government has made repeated claims that it is using evidence to help inform policy. Drawing on the experience of an evaluation of restorative justice (RJ) projects - commissioned by the Youth Justice Board for England and Wales (YJB) - the article concludes that, in this instance, the YJB by-passed an evidence-based approach and gave more priority to developing practice than to the needs of rigorous evaluation. On a more positive note, it is argued that the YJB has recognised the tension between the needs of dynamic policy development and the requirements of rigorous evaluation, and its recent approach to evaluation signals a move towards the latter.