The prospect of pre-emptive self-defence raises serious dilemmas. As long as these remain contested issues (which will be a long time, undoubtedly), they will generate contests over legitimacy. Some of these - by no means exhaustively - can be discussed by reference to specific issues and scenarios. In this context, Draft Principles on the use of self-defence, produced by Chatham House, based on discussions between various informed individuals, including leading authorities (though not, inevitably, reflecting the precise views of all of them), offers useful cues for discussion, followed in the present analysis.6 To do this, the remainder of this analysis reviews the concept of pre-emptive self-defence, then explores relevant aspects of the Draft Principles, as published - first, in relation to notions of prevention, pre-emption and immediacy, then, focusing on necessity, proportionality and the nature of armed attack - and, finally, explores three specific, hypothetical scenarios, derived from the context of the Chatham House project, but not included in the final output, and so used, here, for illustration of issues and critical appraisal of them. 7 In each case, it is evident that no issue is clear and straightforward, and that each point is a matter of interpretation, which, in a time of change, is even more contested than might be the case otherwise.