The concept of a Grotian moment remains rather obscure in international law. On the one hand, it can refer simply to an empirical fact which galvanises the ordinary law-making processes, whether treaty-making or State practice, resulting in major shifts in international law. On the other hand, a Grotian moment might be seen as an event so significant that it results in an extraordinary shift in international law without full adherence to the processes for law-making. The former understanding has little legal significance, while the latter, which would be legally significant, would be controversial and without legal basis. Against this background the article discusses the intersections between peremptory norms and Grotian Moments. It does this by looking at the intersection between the two concepts as well as the intersection between Grotian Moments, on the one hand and, on the other hand, particular jus cogens norms. With respect to the former, for example, the article will consider whether the high threshold of peremptory status facilitates and hinders Grotian moments. With respect to the latter, the article will consider particular norms that have been said to have shifted on account of the Grotian moments, namely the right to use of force in self-defence as well humanitarian intervention.