The impact of cctv systems on crime rates has been more extensively researched in Great Britain than anywhere else. We offer, in this paper, a review of the findings of this systematic effort in evaluation research. The main finding is that a number of necessary conditions must be satisfied for a significant prevention effect to occur: first, an appropriate mobilization of resources invested in the experiments; second, a conceptually adequate specification of relevant, feasible and measurable target outcomes; third, a package of auxiliary but necessary treatment components; fourth, a thorough understanding of the unique ecological attributes of the experimental and control environments. A recurrent pattern in cctv and crime research is that these technological solutions are in fact sensitive to the implementation and actual management contingencies that shape their utilization.