Abstract We develop a model of counterterrorism to analyze the effects of allowing a government agency to torture terrorist suspects. We find that legalizing torture in high evidence cases has offsetting effects on agency incentives to counter terrorism by means other than torture. It increases these incentives because other efforts may increase the probability of having high enough evidence to warrant the use of torture if other efforts fail. However, it also lowers these incentives because the agency might come to rely on torture to avert attacks. If the latter effect dominates, legalizing torture in high evidence cases can reduce security and increase the probability of terrorist attack. Moreover, it can increase agency incentives to torture even in low evidence cases, leading to a "slippery slope." (JEL K4, D8, H1