Most, if not all empirical research on evidence-based policy has three features: firstly, it typically focuses on the application of science and scientific expertise on policy; secondly, it is executed by ‘outsider’ researchers who are not part of the public administration or policy-making process but observers of it (for example, Stevens, 2010); and thirdly, the major topical focus is in social policy areas such as health, education and crime (Oliver et al, 2014). This study advances the perspectives on evidence-based policy making by exploring the role of engineering expertise in policy making. We first make the case that, although related, science and engineering represent different epistemic communities in relation to policy practice. This difference, we argue, can give rise to particular styles of interaction that can make the governance of engineering expertise in policy making different to that for science or scientists. We then report on the findings of a study of the relationship between a new engineering team in a UK ministry with a technical portfolio and the policy colleagues they worked with across a range of programme areas. Through 18 interviews with policy officials, we identify a range of interactions that imply a need to consider styles of management and approaches to internal deployment of experts within policy organisations, as well as the implications for policy making and engineering expertise, given the way policy and engineering practices overlap.<br /><br />Key messages<br /><ul><li>Engineering advice has never been properly identified and studied in the academic social science literature to date.</li><br /><li>Engineering advice is an important and potent source of evidence in policy making in topical areas like energy policy.</li><br /><li>In contrast to science advice, engineering advice as a practice significantly overlaps with policy practice meaning important conflict or complementarity is possible, dependent on how the advice is deployed.</li></ul>