This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book introduces Evidence-Based Policing (EBP) and appraises its underlying philosophy and logic. This involves an incisive discussion on questions such as: What is accepted as evidence and how is it generated? What are the similarities and differences between two dominant approaches that speak to EBP? The chapter proposes alternative research methods to elicit practice-based knowledge from practitioners and to systematise it into evidence. It describes sources of evidence that are available to practitioners, with a particular emphasis on evidence warehouses. The chapter focuses on how evidence syntheses can be made more useful for practitioners in the future by emphasising different aspects of interventions. It discusses the difficulties encountered when trying to inject evidence into police practice. These collectively expose the distance between the optimism of the early adopters of EBP and what the reality is at the coalface of policing.