Interpretation is ubiquitous in legal thought and practice. In international law, the law and method pertaining to the process of interpretation continues to generate rich debates amongst legal scholars and to pose perplexing questions in international legal practice. The Vienna Convention on the Law of Treaties ('VCLT') reflects the premise that interpretation is, or at least can be, a normative process, that is, a formal process based on legal rules. 1 Yet, whilst the VCLT rules are increasingly accepted and relied upon by international courts and tribunals, this does not mean that the law on treaty interpretation is static. In fact, the law of treaty interpretation is still undergoing a process of refinement and progressive development, as attested by recent initiatives within the United Nations International Law Commission ('ILC'). 2 In parallel, the current refocus on the building blocks of international law that is evinced by the work of the ILC calls for a reappraisal of legal interpretation in connection to non-treaty rules. The ILC's earlier work on unilateral acts of states addressed specifically the topic of interpretation and adopted a Guiding Principle to This paper is based on research conducted in the context of the project 'The Rules of Interpretation of Customary International Law' ('TRICI-Law').