This book provides an insightful and nuanced account of the roles of knowledge and evidence in behavioural science practices. Utilising evidence from Australia, it draws together the fields of evidence-based policymaking and behavioural insights in order to examine how policy actors negotiate the use of scientific evidence, knowledge, lived experience, and ethics in policymaking. It also considers the ways in which different knowledges can ‘compete’ in public policy, and the roles of policymakers in that competition. Offering insights for both evidence-based policy processes and the application of behavioural insights more generally, the book is a valuable resource for academics and practitioners interested in behavioural sciences, and the impact of different types of evidence in policymaking.