At its first session, in 1949, the International Law Commission selected the law of treaties as a topic for codification to which it gave priority. The Commission appointed Mr. Brierly (United Kingdom), Lauterpacht (United Kingdom), Fitzmaurice (United Kingdom) and Waldock (United Kingdom) as the successive Special Rapporteurs for the topic at its first (1949), fourth (1952), seventh (1955) and thirteenth (1961) sessions. The Commission considered the topic at its second (1950), third (1951), eighth (1956), eleventh (1959) and thirteenth to eighteenth sessions (1961-1966).
The Commission completed the first reading of the draft articles at its sixteenth session, in 1964. At its seventeenth session, in 1965, the Commission began the second reading of the draft articles in the light of comments by Governments. At its eighteenth session, in 1966, the Commission completed the second reading of the draft articles and adopted its final report on the law of treaties. In submitting the final report to the General Assembly, the Commission recommended that the Assembly should convene an international conference of plenipotentiaries to study the Commission’s draft articles on the law of treaties and to conclude a convention on the subject.
Following the discussion in the Sixth Committee on the report of the Commission on the work of its eighteenth session, the General Assembly by resolution 2166 (XXI) of 5 December 1966, decided to convene an international conference. It requested the Secretary-General to convoke the first session of the conference early in 1968 and the second session early in 1969. By the same resolution, the Assembly invited Member States, the Secretary-General and the Directors-General of those specialized agencies which act as depositaries of treaties to submit their written comments and observations on the draft articles.
By resolution 2287 (XXII) of 6 December 1967, the General Assembly convened the first session of the United Nations Conference on the Law of Treaties at Vienna in March 1968. It was held at the Neue Hofburg in Vienna from 26 March to 24 May 1968, and was attended by representatives of 103 countries and observers from thirteen specialized and intergovernmental agencies. The second session was held from 9 April to 22 May 1969, also at Vienna, and was attended by representatives of 110 countries and observers from fourteen specialized and intergovernmental agencies. The first session of the Conference was devoted primarily to consideration by a Committee of the Whole and by a Drafting Committee of the set of draft articles adopted by the International Law Commission. The first part of the second session was devoted to meetings of the Committee of the Whole and of the Drafting Committee, completing their consideration of articles reserved from the previous session. The remainder of the second session was devoted to thirty plenary meetings which considered the articles adopted by the Committee of the Whole and reviewed by the Drafting Committee.
The Conference adopted the Vienna Convention on the Law of Treaties on 22 May 1969 (status). The Convention was opened for signature on 23 May 1969. It remained open for signature until 30 November 1969 at the Federal Ministry for Foreign Affairs of Austria and, subsequently, until 30 April 1970, at United Nations Headquarters. In addition to the Vienna Convention on the Law of Treaties, the Conference adopted two declarations (the Declaration on the Prohibition of Military, Political or Economic Coercion in the Conclusion of Treaties and the Declaration on Universal Participation in the Vienna Convention on the Law of Treaties) and five resolutions which were annexed to the Final Act of the Conference.
The Vienna Convention on the Law of Treaties codifies the rules that guide treaty relations between States, the term ‘treaty’ being defined for the purposes of the Convention as ‘an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation’. The Convention provides an international legal framework for these relations in times of peace (the effect on treaties of the outbreak of hostilities between States is explicitly excluded from the reach of the Convention). This framework includes the rules on the conclusion and entry into force of treaties, their observance, application, interpretation, amendment and modification, and rules on the invalidity, termination and suspension of the operation of treaties. By providing this legal framework, the Convention promotes the purposes of the United Nations set forth in the Charter, including the maintenance of international peace and security, the development of friendly relations between states and the achievement of cooperation among nations.