This chapter discusses the definition, methods, theories of crime prevention, and the various approaches to the evaluation of crime prevention. Whereas Ekblom distinguishes between crime reduction, which seeks to decrease the frequency and seriousness of criminal events, two other concepts in crime prevention are the notion of displacement and diffusion. Methods of crime prevention have been classified as primary (prevention of the crime event itself); secondary (prevention of criminality by those most at risk of becoming involved); and tertiary (interruption of continued criminality by those already involved). Defensible space proposes that there is a link between the physical environment and crime. According to this theory, features in building design and layouts can increase occupants' vigilance, surveillance opportunities. Methods to evaluate crime prevention interventions range from experimental methodologies, pinnacled by the randomized control trials (RCTs), through to more qualitative approaches.