This paper, in the only long-standing academic series covering situational crime prevention, initiated exploration of the purpose, nature and management of crime prevention knowledge. It arose from my longstanding experience in practical prevention and its evaluation; awareness of failure in government programmes promulgating ‘evidence-based practice’ and interest in research-led demonstration projects; and international interest in ‘good practice’ databases. Viewing knowledge as a means for improving performance, the paper addresses a paradox: over-exact replication of interventions means poor adaptation to new, and different, contexts. The resolution requires treating replication like innovation: practitioners should copy a design-like...