International Law Commission

Last update: June 29, 2023

Summaries of the Work of the International Law Commission

Subsequent agreements and subsequent practice in relation to interpretation of treaties*

*At its sixty-fourth session, in 2012, the Commission decided to change, in 2013, the format of the work on this topic and its title from "Treaties over time" to "Subsequent agreements and subsequent practice in relation to interpretation of treaties".

At its sixtieth session, in 2008, the Commission, on the basis of a recommendation of the Working Group on the long-term programme of work, identified the topic “Treaties over time” for inclusion in its long-term programme of work.¹ A syllabus describing the possible overall structure of, and approach to, the topic was annexed to that year’s report of the Commission.² At the same session, the Commission decided to include the topic in its current programme of work and to establish a Study Group on the topic at its sixty-first session, in 2009.³ The General Assembly, in resolution 63/123 of 11 December 2008, took note of the inclusion of the topic in the Commission’s programme of work.

At its sixty-first session, in 2009, the Commission established a Study Group on Treaties over Time, chaired by Georg Nolte.⁴ At that session, the Study Group focused its discussions on the identification of the issues to be covered, the working methods of the Study Group and the possible outcome of the Commission’s work on the topic.⁵ The Study Group agreed on the following:⁶ (a) work should start on subsequent agreement and practice on the basis of successive reports to be prepared by the Chair for the consideration of the Study Group, while the possibility of approaching the topic from a broader perspective should be further explored; (b) the Chair would prepare for the following year a report on subsequent agreement and practice as addressed in the jurisprudence of the International Court of Justice, and other international courts and tribunals of general or ad hoc jurisdiction; (c) contributions on the issue of subsequent agreement and practice by other interested members of the Study Group were encouraged, in particular on the question of subsequent agreement and practice at the regional level or in relation to special treaty regimes or specific areas of international law; (d) moreover, interested members were invited to provide contributions on other issues falling within the broader scope of the topic as previously outlined. The Commission took note of the oral report of the Chair of the Study Group.⁷

At its sixty-second session, in 2010, the Study Group on Treaties over time was reconstituted, with Mr. Nolte as Chair.⁸ The Study Group began its work on the aspects of the topic relating to subsequent agreements and practice, on the basis of an introductory report prepared by its Chair on the relevant jurisprudence of the International Court of Justice and arbitral tribunals of ad hoc jurisdiction.⁹ Also, the Study Group recommended that a request for information be included in Chapter III of the Commission’s report and be also brought to the attention of States by the Secretariat.¹⁰ The Commission took note of the oral report of the Chair of the Study Group and approved the recommendation concerning the request for information from States.¹¹

At the sixty-third session, in 2011, the Commission reconstituted once again the Study Group on Treaties over time, which continued its work on the aspects of the topic relating to subsequent agreements and practice.¹² The Study Group first completed its consideration of the introductory report by its Chair on the relevant jurisprudence of the International Court of Justice and of arbitral tribunals of ad hoc jurisdiction, by addressing the question of possible modifications of a treaty by subsequent agreements and practice, and the relation of subsequent agreements and practice to formal amendment procedures, and also considered a working paper by Mr. Murase on evolutionary interpretation. The Study Group then began its consideration of the second report by its Chair, dealing with the jurisprudence under special regimes relating to subsequent agreements and practice, by focusing on certain conclusions contained in the report. In the light of the discussions, the Chair of the Study Group reformulated the text of nine preliminary conclusions on a number of issues including reliance by adjudicatory bodies on the general rule of treaty interpretation, different approaches to treaty interpretation, and various aspects concerning subsequent agreements and practice as a means of treaty interpretation.¹³ The Commission took note of the oral report of the Chair of the Study Group and approved the recommendation that States be invited again to provide information in relation to the topic.¹⁴

At its sixty-fourth session, in 2012, the Commission decided to change, with effect at the sixty-fifth session, the format of the work on this topic and its title as suggested by the Study Group. The Commission also decided to appoint Mr. Nolte as Special Rapporteur for the topic “Subsequent agreements and subsequent practice in relation to interpretation of treaties”.¹⁵

At the sixty-fifth session in 2013, the Commission had before it the first report of the Special Rapporteur,¹⁶ which, inter alia, contained four draft conclusions relating to the general rule and means of treaty interpretation; subsequent agreements and subsequent practice as means of interpretation; the definition of subsequent agreement and subsequent practice as means of treaty interpretation; and attribution of a treaty related practice to a State.¹⁷ Following the debate in plenary, the Commission decided to refer the four draft conclusions to the Drafting Committee. Upon consideration of the report of the Drafting Committee, the Commission provisionally adopted draft conclusions 1 to 5, together with commentaries thereto.¹⁸

At the sixty-sixth session in 2014, the Commission had before it the second report of the Special Rapporteur,¹⁹ in which the Special Rapporteur considered the following aspects of the topic: the identification of subsequent agreements and subsequent practice; possible effects of subsequent agreements and subsequent practice in the interpretation of treaties; the form and value of subsequent practice under article 31, paragraph 3 (b); the conditions for an “agreement” of the parties regarding the interpretation of a treaty under article 31, paragraph 3; decisions adopted within the framework of Conferences of States Parties; and the possible scope for interpretation by subsequent agreements and subsequent practice. The report also included some information on the future programme of work.²⁰ The Special Rapporteur proposed draft conclusions 6 to 11, which were subsequently referred to the Drafting Committee. On the basis of the report of the Drafting Committee, the Commission provisionally adopted five draft conclusions, with commentaries thereto.²¹

At the sixty-seventh session in 2015, the Commission had before it the third report of the Special Rapporteur,²² which contained, inter alia, one draft conclusion relating to constituent instruments of international organizations. The Commission subsequently provisionally adopted draft conclusion 11, on the basis of the report of the Drafting Committee, together with a commentary thereto.²³

At its sixty-eighth session, in 2016, the Commission had before it the fourth report of the Special Rapporteur,²⁴ addressing the legal significance, for the purpose of interpretation and as forms of practice under a treaty, of pronouncements of expert bodies and of decisions of domestic courts. The report proposed draft conclusions 12 and 13 on those issues. It also discussed the structure and scope of the draft conclusions, proposed the inclusion of a new draft conclusion 1a, and suggested a revision to draft conclusion 4 (3).²⁵ The Commission referred draft conclusions 1a and 12, as presented by the Special Rapporteur, to the Drafting Committee.²⁶

Following presentation and consideration of the report of the Drafting Committee, the Commission adopted, on first reading, a set of 13 draft conclusions, together with commentaries thereto. In accordance with articles 16 to 21 of its Statute, the Commission transmitted the draft conclusions, through the Secretary-General, to Governments for comments and observations, with the request that such comments and observations be submitted to the Secretary-General by 1 January 2018.²⁷

At its seventieth session, in 2018, the Commission had before it the fifth report of the Special Rapporteur,²⁸ as well as comments and observations received from Governments.²⁹ The Commission commenced the second reading of the draft conclusions on subsequent agreements and subsequent practice in relation to the interpretation of treaties and subsequently adopted, on second reading, a set of 13 draft conclusions, together with commentaries thereto, on subsequent agreements and subsequent practice in relation to the interpretation of treaties. In accordance with article 23 of its statute, the Commission recommended that the General Assembly (a) take note in a resolution of the draft conclusions on subsequent agreements and subsequent practice in relation to the interpretation of treaties, annex the draft conclusions to the resolution, and ensure their widest dissemination; and (b) commend the draft conclusions, together with the commentaries thereto, to the attention of States and all who may be called upon to interpret treaties.³⁰

The final draft consists of thirteen draft conclusions divided into four parts: Part One. Introduction (conclusion 1); Part Two. Basic rules and definitions (conclusions 2–5); Part Three. General aspects (conclusions 6–10; and Part Four. Specific aspects (conclusions 11–13).

By resolution 73/202 of 20 December 2018, the General Assembly took note of the conclusions on subsequent agreements and subsequent practice in relation to the interpretation of treaties, the text of which was annexed to the resolution, with the commentaries thereto, brought them to the attention of States and all who may be called upon to interpret treaties and encouraged their widest possible dissemination.

¹ See Yearbook … 2008, vol. II (Part Two), paras. 351–352.

² See ibid., Annex I.

³ See ibid., para. 353.

⁴ See Yearbook … 2009, vol. II (Part Two), para. 218.

⁵ See ibid., paras. 220–226.

⁶ See ibid., para. 226.

⁷ See ibid., para. 219.

⁸ See Yearbook … 2010, vol. II (Part Two), para. 345.

⁹ See ibid., paras. 347–352.

¹⁰ See ibid., para. 354.

¹¹ See ibid., para. 346.

¹² See Yearbook … 2011, vol. II (Part Two), paras. 334–343.