This chapter seeks to fill the gap – to understand what is meant by technology and to relate it to key concepts in situational crime prevention (SCP). It considers the nature of technology. The chapter examines how technology relates to opportunity, problems and solutions. It also examines how technology relates to opportunity, problems and solutions. The chapter covers both traditional frameworks of SCP and a more integrated and detailed counterpart, the Conjunction of Criminal Opportunity. It also examines the relationship between crime and technological change, covering adaptations and conflicts over longer timescales, viewed as arms races between offenders and preventers and drawing on ideas from biological and cultural evolution. Co-evolution through conflict, as just described, constitutes a powerful accelerant of technological change in both criminal and military arenas since the two opposing sides focus sharply, consistently and persistently on countering one another's resources and capabilities.