The concept of countermeasures Countermeasures are coercive measures taken by a responding state (or other actor) against a target state (or other actor) in response to a wrongful act for which the targeted actor bears responsibility. They have become fairly rare today, but remain a conceptually important feature of the arsenal of ‘law enforcement concepts’. As a broad rule, general international law permits countermeasures as a flexible means of responding to previous wrongful conduct, but submits their exercise to a range of procedural and substantive conditions. If these conditions are met, the countermeasure functions as a ‘justification’ or – in the terminology of the International Law Commission (ILC) – a circumstance precluding the wrongfulness of the conduct. In the words of Article 22 of the 2001 Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA): The wrongfulness of an act of a State not in conformity with an international obligation towards another State is precluded if and to the extent that the act constitutes a countermeasure taken against the latter State in accordance with chapter II of part three. The essence of that provision is taken up in Article 22(1) of the 2011 Articles on the Responsibility of International Organizations (ARIO), addressing countermeasures taken by international organisations. However, Article 22(2) ARIO adds that: an international organization may not take countermeasures against a responsible member State or international organization [under the conditions referred to in paragraph 1] unless: This suggests that the general law of countermeasures – binding as customary international law and in many respects reflected in the ILC’s two sets of Articles – interacts with special treaty regimes; it is subsidiary to treaty-specific ‘means … for otherwise inducing compliance with the obligations of the responsible State or international organization’. Beyond that, as a feature of the general law of responsibility, countermeasures can be modified or contracted out by special treaties. Because ‘[c]ountermeasures are a feature of a decentralized system’, they are affected by processes of institutionalisation and/or centralisation. ‘[R]ules of the organization’ (in the words of Article 22(2) of the ARIO) can no doubt impose restrictions. More generally, specific treaty regimes may add further conditions or may exclude countermeasures altogether.