Making better use of evidence is essential if public services are to deliver more for less. Central to this challenge is the need for a clearer understanding about standards of evidence that can be applied to the research informing social policy. This paper reviews the extent to which it is possible to reach a workable consensus on ways of identifying and labelling evidence. It does this by exploring the efforts made to date and the debates that have ensued. Throughout, the focus is on evidence that is underpinned by research, rather than other sources of evidence such as expert opinion or stakeholder views.