The Vienna Convention on the Law of Treaties: Codification, Conclusion and Application in Disputes

The Vienna Convention on the Law of Treaties brought rules for creating, interpreting and ending treaty relationships between states into a common text. The International Law Commission selected the law of treaties for codification in 1949, with Brierly, Lauterpacht and Fitzmaurice successively serving as special rapporteurs. The form of the work changed: Fitzmaurice favoured an explanatory code, while Humphrey Waldock, who took over in 1961, was instructed to prepare articles capable of forming the basis of a convention.

In its 1966 report, the Commission explained that a convention would also allow states newly entering the international community to participate directly in making the rules. Written governmental comments and discussions in the General Assembly's Sixth Committee fed into revision. In 1966, the Commission completed its articles and commentaries and recommended a plenipotentiary conference. The rules thus passed through expert drafting, governmental feedback and diplomatic negotiations.

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The UN Conference on the Law of Treaties met in two sessions at Vienna's Neue Hofburg, in March–May 1968 and April–May 1969, attended by 103 and 110 countries respectively. Italy's Roberto Ago presided, Nigeria's Taslim Elias chaired the Committee of the Whole, and Iraq's Mustafa Kamil Yasseen chaired the Drafting Committee. Waldock served as expert consultant.

The Committee of the Whole examined the draft, and the Drafting Committee organized and harmonized the text. Universal participation and dispute-settlement procedures became major issues in the conference's later stages, with delegations retaining reservations about the package compromise. On 22 May 1969, the convention was adopted by 79 votes to one, with nineteen abstentions; France voted against. Support for the final text did not mean every state was satisfied with every provision.

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The convention opened for signature on 23 May 1969, initially at Austria's Federal Ministry for Foreign Affairs and subsequently at UN Headquarters in New York, with the signature period ending on 30 April 1970. Article 82 expressly required ratification and deposit of instruments with the UN Secretary-General; Article 83 provided a separate route of accession. A representative's signature authenticating the text and a state's completion of ratification and consent to obligations cannot be treated as the same stage.

Under Article 84, the convention entered into force on the thirtieth day after deposit of the thirty-fifth instrument of ratification or accession, in practice 27 January 1980. Effective dates were calculated separately for states ratifying or acceding later. Article 4 limited the convention's own temporal application while preserving rules of international law existing independently of it, so all earlier treaties could not simply be subjected to retroactive application.

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Articles 1 and 2 defined the convention's subject as written agreements between states governed by international law, regardless of their designation. Article 3 preserved the legal force of agreements outside that scope. Alongside methods of expressing consent, such as signature, ratification and accession, the convention required treaties in force to be performed in good faith and generally prevented reliance on domestic law to justify non-performance.

Article 31 required good-faith interpretation of the ordinary meaning of terms in context and in light of a treaty's object and purpose, also taking account of qualifying subsequent agreements, subsequent practice and relevant rules of international law. Article 32 permitted recourse to preparatory work and the circumstances of conclusion to confirm meaning or resolve ambiguity, manifest absurdity and related problems. Negotiating records could therefore inform interpretation, but had to be connected with the formal provisions and their context.

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The convention did not treat every signed instrument as valid. Article 52 addressed treaties procured by the threat or use of force contrary to UN Charter principles; Article 53 addressed treaties conflicting at conclusion with peremptory norms of general international law. These rules limited what states could lawfully arrange by agreement, so signatures by both parties could not alone preclude scrutiny.

For existing treaties, Articles 61 and 62 respectively limited grounds such as impossibility of performance and fundamental change of circumstances. A party invoking invalidity, withdrawal or termination also had to notify the other parties and state its reasons under Article 65. Article 66 provided judicial, arbitral or conciliation routes for specified disputes. Peremptory-norm disputes and other disputes under Part V followed different procedures; this did not mean that every treaty disagreement automatically went to the International Court of Justice.

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In 1997, the International Court of Justice tested these rules in the Gabčíkovo–Nagymaros Project case between Hungary and Slovakia, concerning a 1977 treaty for waterworks on the Danube. The Court noted that both states had ratified the Vienna Convention after conclusion of that treaty, preventing direct application of the convention. Articles 60–62 nevertheless reflected customary international law in many respects and could be used to examine grounds for termination.

Hungary invoked changes in political and economic conditions and environmental understanding, among other reasons. After examining them individually, the Court held that they had not fundamentally altered the obligations still to be performed and that Hungary's 1992 termination notice had not ended the original treaty's legal effects. The judgment showed that invoking convention rules required an explanation of the legal basis, facts and procedures. The provisions supplied a framework for judgment but could not replace states' actual performance of their obligations.

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