Sometimes, states face emergencies: situations where many individuals face an imminent threat of serious harm. Some believe that in such cases certain sorts of actions which are normally morally prohibited might be permissible. In this paper, I discuss this view as it applies in both the contexts of war and of public health policy. I suggest that the deontologist can best understand emergencies by analogy with the distinction between act- and rule consequentialism. In real world cases, we must often make decisions in ‘epistemically murky’ situations, such that the application of deontological principles to particular cases is unclear. I suggest that we develop conventions to deal with such cases in a manner which we think is most likely to approximate the demands of abstract deontological principles across time. I claim that we can best understand ‘supreme emergencies’ as situations which ‘epistemic murkiness’ is resolved. In such cases, there may be a conflict between what would be valid application of abstract deontological principles and the conventions which normally guide us in epistemically murky situations.