This article applies formal modeling to study a terrorist group's choice of whether to attack or not, and, in the case of an attack, which of two potential targets to strike. Each potential target individually takes protective measures that influence the terrorists' perceived success and failure, and, hence, the likelihood of attack. For domestic terrorism, a tendency for potential targets to overdeter is indicated. For transnational terrorism, cases of overdeterrence and underdeterrence are identified. We demonstrate that increased information about terrorists' preferences, acquired by the targets, may exacerbate inefficiency when deterrence efforts are not coordinated. In some cases, perfect information may eliminate the existence of a noncooperative solution.