The interest in crime prevention on the part of international organizations raises important questions about the usefulness of criminological knowledge in the policy-making context. Two models can be identified: the evidence-based model, advocated by the Campbell Collaboration, and the reflexive model, envisioned by George Soros’s Open Society foundations network. Although both models reference ideas of Karl Popper, neither makes full use of his social philosophy. Popper has more to offer criminology than the idea of falsification. His concepts of social situation, social tinkering, and open society emphasize the important methodological principle of learning from mistakes. If policy makers, and the criminologists who hope to advise them, are interested in pursuing crime prevention within a multinational open society, they should take into account the self-organizing aspect of science, the normality of accidents in social affairs, and the politics of social science research.