This paper is part of an edited collection on evaluation and the new public management commissioned by Elsevier in their Advances in Program Evaluation series. The paper discusses trust and evaluation. It considers the nature of trust and the ways in which it has been undermined by the accountability relationships characteristic of the new public management. The paper argues that as evaluation has become institutionalised it invites strategic action that can deceive and distort organisational goals. The paper concludes by exploring the social foundations of evaluation and the importance of reciprocity, respect and trust to effective evaluation. Although trust is of considerable importance to the practice of evaluation, it has received very little attention in the literature on educational evaluation or the wider literature on programme and policy evaluation. This is the first systematic treatment of trust in the context of evaluation. It is a contribution to evaluation theory.