This article reviews the evidence on the deterrent effect of police, imprisonment, and capital punishment and additionally summarizes knowledge of sanction risk perceptions. Studies of changes in police presence, whether achieved by changes in police numbers or in their strategic deployment, consistently find evidence of deterrent effects. Studies of the deterrent effect of increases in already long prison sentences find at most a modest deterrent effect. Studies of the deterrent effect of capital punishment provide no useful information on the topic. Four high-priority areas for future research are identified: developing and testing an integrated model of the effects of the threat and experience of punishment, measuring perceptions of sanction regimes, developing and testing a theory of criminal opportunities, and estimating the deterrent effect of shorter prison sentences and identifying high-deterrence policies.