Knowledge and evidence are not synonyms, despite often being used in this way. Evidence is knowledge that is labelled in a political act. It does not simply appear in policy but is produced, contested, and advocated for in policy processes. Chapter 4 explores how different types of knowledge compete in behavioural insights, and the role of policy actors in that competition as they make and unmake evidence. It explores the tensions that emerge between policy actors in contests over what counts as evidence and who claims the authority to use knowledge in behavioural insights. It reflects on situated agency as a concept to understand the ways in which policy actors are both shaping and shaped by knowledge in behavioural insights.