Preventive use of force may be defined as the initiation of military action in anticipation of harmful actions that are neither presently occurring nor imminent. This essay explores the permissibility of preventive war from a cosmopolitan normative perspective, one that recognizes the basic human rights of all persons, not just citizens of a particular country or countries. It argues that preventive war can only be justified if it is undertaken within an appropriate rule-governed, institutional framework that is designed to help (...) protect vulnerable countries against unjustified interventions while also avoiding unacceptable risks of the costs of inaction. The key to ensuring the fairness of rules governing the preventive use of force is accountability.This essay proposes a scheme that would make those promoting and those rejecting the preventive use of force more accountable. The proposal contains the following crucial features:States proposing preventive war are required to enter into a contract with a diverse body of states as a condition for authorization of their actions;Prior to taking preventive action, states must make an evidence-based case to the UN Security Council, and agree in advance to submit themselves to an evaluation by an impartial body after the preventive action occurred;Both proponents of action and those opposing it will be held accountable ex post for the accuracy of their prior statements and the proportionality of their actions;Sanctions will be imposed against intervening states or states that opposed preventive action, respectively, depending on the findings of the ex post evaluation.If preventive action were blocked in the Security Council, states seeking to engage in preventive action could then present their case in a different body–a coalition of democratic states–with its own ex post and ex ante accountability procedures. (shrink)