Anthropologists have become increasingly concerned about the discipline's lack of ‘public engagement’ with contemporary issues of late, but a key underlying problem - anthropology's unwillingness to address the nature and evidentiary status of anthropological knowledge itself - has remained largely unacknowledged. Here I approach this problem initially through an analysis of the rise of ‘evidence’ as a central concept in public policy and practice. Using the exemplar of ‘evidence-based’ medicine, I analyse anthropological responses to these evidentiary requirements, arguing that this turn to evidence can be seen in many other arenas of research and public policy and presents a fundamental challenge for the credibility and legitimacy of anthropology as a discipline. In the second part of the article comparison with anthropological work on legal issues provides a reflexive opening through which to begin to consider the nature of anthropological ‘evidence’ itself.