When negotiating states introduced the notion of peremptory norms or ius cogens norms into the 1969 Vienna Convention on the Law of Treaties (VCLT), they foresaw a specific mechanism for settling disputes that referred to an alleged breach of a peremptory norm of general international law (ius cogens norm) as grounds for voiding or terminating a treaty, circumstances specifically provided for in Articles 53 and 64 of the Convention. Indeed, paragraph (a) of Article 66 provides that such disputes should be submitted to arbitration or to the International Court of Justice (ICJ).1 It was considered appropriate, therefore, that when settling such disputes, courts should address the question of how the effects of peremptory norms of general international law specifically apply to treaties.2