This chapter focuses on policy evaluation, defined as the assessment of a public policy to determine whether it has achieved its objectives. We discuss two types of policy evaluation: expert evaluation and participatory evaluation. While expert styles insist on the technicality of policy evaluations and on scientific sophistication, participatory styles focus on the integration of policy stakeholders and laypersons during the evaluative process. Because expert evaluation styles are marked by their scientific character and independence, they enjoy a high internal reliability and a result-based legitimacy. In contrast, core features of participatory evaluation styles are their representativeness and transparency, which is associated with external reliability and a process-based legitimacy. The chapter outlines the historical development of these two evaluation styles and discusses their respective strengths and weaknesses in the light of contemporary decision-making processes. Finally, we discuss the risks associated with technocratic policy evaluation styles on the one hand, and politicized participatory evaluations on the other hand, in the context of post-truth democracy.