This chapter discusses the miscarriages of justice, the focal point of driving change in any criminal justice system, through the identification of failure. It also discusses the need to protect the vulnerable and facilitate their involvement in the justice system. The chapter focuses on a distinct area of investigation, discussing the impact of psychological theory on witness testimony. It argues that a relatively new concepts of Evidence Based Policing and Evidence Based Police Training and looks at three countries, providing evidence that there is a positive move towards training that incorporates empirical knowledge. The study of human behaviour related to crime and justice commenced more than 100 years ago when pioneer psychologists wrote about the reliability of witnesses and the confessions of suspects, in court cases. The chapter also presents an overview of the key concepts discussed in this book.