Effective and efficient crime investigation and detection complement preventive approaches in containing criminal activity. A good record on detecting crime is important for maintaining public confidence in policing services, since victims and other citizens expect culprits to be brought to justice. Policing provides deterrence through the offender’s fear of being caught (von Hirsch et al. 1999)—the same threat that underlies prevention via guardianship or guardianship objects, much of which is aligned with routine activity theory (Cohen and Felson 1979). Even with existing levels of crime investigation and detection in combination with preventive approaches, crimes of all types—property, violent and sexual—persist in substantial quantities in many developed countries, not least in Australia and the UK, where most of the evidence presented in this volume originates. Preventive approaches appear unlikely to be capable of combating offending alone without effective police capacity to detect crime. Cost-effective crime investigation and detection is not merely important; it is an indispensable part of any crime reduction strategy, both directly in terms of the arrest and rehabilitation of criminals and indirectly through deterrence and enhancing perceptions of police professionalism and legitimacy.