The chapter first describes psychological research that has shaped the legal and regulatory framework for custodial questioning of suspects in England and Wales. Psychological research has been consulted in addressing the issues of interviewee suggestibility and low intelligence, as well as behavioral dynamics that lead to false confessions. Psychological research has also challenged an investigative culture that relies too much on confession evidence, and it has contributed to law reform related to the "right to silence" in the face of police questioning. The second section of the chapter presents an overview of some of the psychological processes involved in the construction of testimony. This includes research on the cognitive and social influences that shape memory of events, which has significant implications for the reliability of witness testimony, particularly eyewitness testimony about events and the physical characteristics of people. The third section of the chapter discusses the influence of psychological research on the creation and functions of police behavioral science units in the areas of crime-scene assessment, predictive profiling of offenders, the prioritizing of suspects, suggestions for the direction of investigations, investigative interviewing strategies, media strategies, and familial DNA prioritization. In conclusion, the author advises that if investigative psychology is to improve its use in criminal investigations, it will require the data, databases, network, and analytical tools that will promote a progression from traditional deductive investigations to inductive, knowledge-based investigations. This begins with the collection of accurate and reliable information that will make possible such a paradigm shift. 77 references