Whether states can use force against terrorists based in another country is much discussed. The relevant provisions of the UN Charter do not provide a conclusive answer, but have to be interpreted. The present article suggests that in the course of the last two decades, the Charter regime has been re-adjusted, so as to permit forcible responses to terrorism under more lenient conditions. In order to illustrate developments, it juxtaposes international law as of 1989 to the present state of the law. It argues that the restrictive approach to anti-terrorist force obtaining 20 years ago has come under strain. As far as collective responses are concerned, it is no longer disputed that the Security Council could authorize the use of force against terrorists; however, it has so far refrained from doing so. More controversially, the international community during the last two decades has increasingly recognized a right of states to use unilateral force against terrorists. This new practice is justified under an expanded doctrine of self-defence. It can be explained as part of a strong international policy against terrorism and is part of an overall tendency to view exceptions to the ban on force more favourably than 20 years ago. Conversely, it has led to a normative drift affecting key limitations of the traditional doctrine of self-defence, and increases the risk of abuse. © The European Journal of International Law Vol. 20 no. 2 EJIL 2009; all rights reserved.