Chapter 9 delves into juridical military necessity as an exception. It begins by distinguishing juridical military necessity from the state of necessity, a circumstance precluding the wrongfulness of an act under the international law of state responsibility, on account of their distinct normative status and distinct contents. The discussion then proceeds to the four cumulative requirements customary IHL imposes when invoking express military necessity clauses. First, the measure must be taken as primary for some specific military purpose. Second, the measure must be ‘required’ for the purpose’s attainment. This requirement may be sub-divided into three components, namely relevance, minimum injury and proportionality. Third, the purpose must itself conform to IHL. Fourth, the measure must also conform to IHL.