Treaty interpretation is central to the work of international lawyers. One of the principal tools used by the International Section attorneys for this purpose is the 1969 Vienna Convention on the Law of Treaties. The convention, which is based on draft articles prepared by the International Law Commission, applies to agreements between countries and is widely regarded as codifying customary international law on treaties with some necessary augmentations and clarifications. It entered into force on 27 January 1980 and has been ratified by 108 countries as of 2008. While the U.S. signed the Convention on May 26, 1971, the Senate has never given its advice and consent to ratification. Nevertheless, the U.S. generally recognizes the Convention as an authoritative restatement of customary international law. See, e.g., Assistant Legal Advisor for Treaty Affairs at the Department of State and Secretary of State Roger’s Report to the President offsite link, Oct. 18, 1971, 65 Dep’t St. Bull. 684, 685 (1971); Chubb & Son, Inc. v. Asiana Airlines offsite link, 214 F.3d 301, 308 (2nd Cir. 2000) (cert. denied).

Additional reference information: 

• Vienna Convention on the Law of Treaties offsite link
• List of countries offsite link that have ratified the Convention, including any reservations entered.
• Treaty Doc. 92-12. Message from the President of the United States to the U.S. Senate transmitting the Vienna Convention on the Law of Treaties for advice and consent to ratification (November 22, 1971)
• S. Prt. 106-71 (106th Cong, 2d Sess.) Treaties and Other International Agreements: The Role of the United States Senate. A Study Prepared for the Senate Foreign Relations Committee by the Congressional Research Service (January 2001).
• International Law Commission Draft Articles offsite link on the Law of Treaties with commentaries, 1966
• United Nations offsite link Conference on the Law of Treaties, 1968-1969
• UN Treaty Reference Guide offsite link, Definition of Key Terms. (downloadable PDF version)
• International Law of Treaties offsite link
• Congressional Research Service, International Law and Agreements: Their Effect Upon U.S. Law (Jan. 26, 2010).
• IMO offsite link, Adopting a convention, Entry into force, Accession, Amendment, Enforcement, Tacit acceptance procedure
• International Law Commission, Treaties over Time/Subsequent Agreements and Subsequent Practice in Relation to Interpretation of Treaties offsite link, and Formation and Evidence of Customary International Law offsite link
• Northwestern Law School, United States Treaty Research offsite link