The September 11 terrorist strikes prompted renewed interest in a debate about just cause that has been increasingly open since the demise of the Cold War and the shift to a more multilateral and interventionist world order. This article contributes to that debate by looking first into the just war tradition to argue for a conceptual revision that equates just cause with jus ad bellum (just recourse to war). It then seeks to specify the component parts of just cause understood in this way, holding that demonstrable injustice should take the place formerly occupied by just cause in just war theory. Towards the end it uses three real-world cases to develop a mechanism for validating just cause claims. The argument is that a cause is just only when its proponents can convince an international forum of intractable injustice, responsible intervention, and an appropriate balance of contingent factors. The article closes by considering how the current war on terrorism might be assessed in such a forum.