The concept of evidence-based policy (EBP) and the ethical challenges it poses are explored. First a ‘standard’ model of EBP is outlined and implicit assumptions it makes about the nature of evidence and the policy-making process are examined. Debates about how best to implement EBP in the criminal justice sector are investigated before various critiques of EBP are discussed. These start with methodological debates relating to the generation of empirical evidence and how to review evidence, but a set of ethical concerns soon emerge. These are not abstract, academic debates. Using the example of different approaches to offender rehabilitation the practical dimensions of such ethical concerns are demonstrated using offender rehabilitation as an example.