This chapter frames the interpretive regime of modern international law as a historical contingency and aims to trace its genealogy through an analysis of the codification process that led to the current regime. The contingency of the rules of treaty interpretation is hardly recognized in the official discourse. Treated as a matter of common sense or trans-historical customary international law, the rules of treaty interpretation set forth in the Vienna Convention on the Law of Treaties have for instance been applied to the interpretation of treaties dating back to the nineteenth century and a whole range of treaties concluded in the twentieth century before the entry into force of the Vienna Convention. There is, however, ample evidence that the interpretive approach of the Vienna Convention has by no means prevailed throughout the history of international law. This chapter identifies a series of factors ranging from the intellectual history of the discipline of international law and the contingencies of the codification process, to the political circumstances of the Cold War era and the rise of permanent international tribunals that can account for the normative outcome of the Vienna Convention regime.

This chapter examines the process whereby the concept of jus cogens was introduced into international law during the 1968–69 Vienna Conference on the Law of Treaties. The 1969 Vienna Convention on the Law of Treaties, the conference’s final product, declared that some rules of international law command universal authority, with Article 53 recognizing ‘peremptory norms of general international law’ (without specifying which norms counted as such). Yet the negotiations through which jus cogens entered into the law of treaties were marked by wide-ranging debates about the nature and limits of the treaty-making power, and ultimately about the basic structure and orientation of international law more generally. On the one hand were lawyers and diplomats from socialist and nonaligned states for whom the concept was potentially useful as a means of undercutting the legality of unequal treaties, colonial concession agreements, and other substantively unjust instruments. On the other hand were lawyers and diplomats from industrialized countries who were committed to the traditional principle of pacta sunt servanda—the ‘sanctity of compacts’—and deeply skeptical of any attempt to introduce a normative spectrum in which a select group of rules would have controlling authority over all others.