This chapter is devoted to the evidence from Crime Science that underpins the effectiveness of Situational Crime Prevention (SCP), Crime Prevention Through Environmental Design (CPTED) and Designing Out Crime (DOC). Until close to the end of the twentieth century, it was extremely rare to find the original practitioners of DOC (Architectural Liaison Officers and Crime Prevention Design Advisers as they were then known in the UK context) citing such evidence to support the recommendations they were making. This was especially the case in a policing environment. However, over little more than a quarter century a sea-change has taken place. Propelled by the concepts of evidence-based policing and crime prevention (Farrington et al, 2002; Ekblom, 2011a) DOC now actively seeks out evidence to justify the measures being recommended. Beginning with an examination of Crime Displacement and Diffusion of Benefits, the chapter covers a wide arena of Crime Science subjects believed to be of practical relevance to the Designing Out Crime Officer (DOCO) or CPTED Officer/Adviser. These include Routine Activity Theory, Crime Opportunity, Rational Choice Theory, Crime Opportunity, Problem Oriented Policing, Problem Solving and many more.