Knowledge and non-knowledge are equally constitutive for political decisionmaking. The relationship between what we know, what we do not know, what we cannot know and what we do not like to know determines the cognitive frame for political practice. This article analyses how uncertainty is perceived and how danger is constructed in the global `war on terror'. We fist identify threats, risks, catastrophes and ignorance as distinct kinds of danger. We then demonstrate how different notions of probability are used to determine their magnitude and to assign political responsibility. In the third part, we show how these `logics of danger' play out in current anti-terror strategies. Security policy in general and the `war on terror' in particular can only be explained, we argue, if ways of managing non-knowledge are taken into account.