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Last update: July 16, 2024

Summaries of the Work of the International Law Commission

Identification of customary international law*

*At its sixty-fifth session, in 2013, the Commission decided to change the title of the topic from "Formation and evidence of customary international law" to "Identification of customary international law".

See also: Analytical Guide | Texts and Instruments

At its sixty-third session, in 2011, the Commission, on the basis of a recommendation of the Working Group on the long-term programme of work, identified the topic “Formation and evidence of customary international law” 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

The General Assembly, in resolution 66/98 of 9 December 2011, took note of the inclusion of the topic in the long-term programme of work of the Commission.

At its sixty-fourth session, in 2012, the Commission decided to include the topic “Formation and evidence of customary international law” in its programme of work and appointed Michael Wood as Special Rapporteur for the topic.3

At its sixty-fifth session, in 2013, the Commission had before it the first report of the Special Rapporteur,4 as well as a memorandum of the Secretariat on the topic.5 The Commission decided to change the title of the topic to “Identification of customary international law”.6

At the sixty-sixth session in 2014, the Commission had before it the second report of the Special Rapporteur, which focused on two constituent elements of rules of customary international law, “a general practice” and “accepted as law”, and proposed 11 draft conclusions.7 The Commission referred the 11 draft conclusions, as contained in the second report, to the Drafting Committee. The Drafting Committee presented its interim report on the topic, containing the eight draft conclusions provisionally adopted by the Drafting Committee, which was presented to the Commission for information only.8

At the sixty-seventh session in 2015, the Commission had before it the third report of the Special Rapporteur,9 which contained, inter alia, additional paragraphs to three of the draft conclusions proposed in the second report and five new draft conclusions.10 The Commission subsequently took note of draft conclusions 1 to 16 [15] provisionally adopted by the Drafting Committee at the sixty-sixth and sixty-seventh sessions.11 The Commission also requested the Secretariat to prepare a memorandum concerning the role of decisions of national courts in the case-law of international courts and tribunals of a universal character for the purpose of the determination of customary international law.12

At its sixty-eighth session, in 2016, the Commission had before it the fourth report of the Special Rapporteur, an addendum to that report providing a bibliography on the topic,13 and a memorandum by the Secretariat on the topic.14 The fourth report contained suggestions for the amendments of the draft conclusions provisionally adopted in light of the comments received by Governments and others. The report also addressed ways and means to make the evidence of customary international law more readily available.15

Following consideration of the fourth report of the Special Rapporteur, as well as of the memorandum by the Secretariat, the Commission referred to the Drafting Committee the proposed amendments to the draft conclusions contained in the fourth report.16 The Commission considered and adopted the report of the Drafting Committee on draft conclusions 1 to 16, thus adopting a set of 16 draft conclusions on the topic on first reading, together with commentaries thereto.17 The Commission also established an open-ended working group, chaired by Marcelo Vázquez-Bermudez, to assist the Special Rapporteur in the preparation of the draft commentaries to the draft conclusions.18 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 2018.19

Also at its sixty-eighth session, the Commission requested the Secretariat to prepare a memorandum on ways and means for making the evidence of customary international law more readily available, which would survey the present state of the evidence of customary international law and make suggestions for its improvement.20

At its seventieth session, in 2018, the Commission had before it the fifth report of the Special Rapporteur, which addressed the comments and observations made by States on the draft conclusions and commentaries adopted on first reading, as well as ways and means for making the evidence of customary international law more readily available.21 The Commission also had before it an updated bibliography on the topic contained in an addendum to that report,22 the comments and observations received from Governments,23 and the memorandum by the Secretariat on ways and means for making the evidence of customary international law more readily available.24

Following consideration of the fifth report of the Special Rapporteur, the Commission referred draft conclusions 1 to 16 to the Drafting Committee, with the instruction that the Drafting Committee commence the second reading of the draft conclusions on the basis of the proposals of the Special Rapporteur, taking into account the comments and observations of Governments and the debate in plenary on the Special Rapporteur’s report.25

The Commission considered the report of the Drafting Committee and adopted the entire set of draft conclusions on identification of customary international law on second reading, together with commentaries thereto. The Commission had also established a working group, chaired by Marcelo Vázquez-Bermudez, to assist the Special Rapporteur in the preparation of the draft commentaries to the draft conclusions. In addition, the Commission requested that the memorandum by the Secretariat on ways and means for making the evidence of customary international law more readily available be reissued to reflect the text of the draft conclusions and commentaries adopted on second reading.26

In accordance with article 23 of its Statute, the Commission decided to recommend that the General Assembly: (a) take note in a resolution of the draft conclusions on identification of customary international law, annex the draft conclusions to the resolution, and ensure their widest dissemination; (b) commend the draft conclusions, together with the commentaries thereto, to the attention of States and all who may be called upon to identify rules of customary international law; (c) note the bibliography prepared by the Special Rapporteur; (d) note the Secretariat memorandum on ways and means for making the evidence of customary international law more readily available, which surveyed the state of evidence of customary international law and made suggestions for its improvement; (e) follow up the suggestions in the Secretariat memorandum by: (i) calling to the attention of States and international organizations the desirability of publishing digests and surveys of their practice relating to international law, of continuing to make the legislative, executive and judicial practice of States widely available, and of making every effort to support existing publications and libraries specialized in international law; (ii) requesting the Secretariat to continue to develop and enhance United Nations publications providing evidence of customary international law, including their timely publication; and (iii) also requesting the Secretariat to make available the information contained in the annexes to the memorandum on ways and means for making the evidence of customary international law more readily available through an online database to be updated periodically based on information received from States, international organizations and other entities concerned.27

The final draft consists of sixteen draft conclusions divided into seven parts: Part One. Introduction (conclusion 1); Part Two. Basic approach (conclusions 2–3); Part Three. A general practice (conclusions 4–8); Part Four. Accepted as law (opinio juris) (conclusions 9–10); Part Five. Significance of certain materials for the identification of customary international law (conclusions 11–14); Part Six. Persistent objector (conclusion 15); and Part Seven. Particular customary international law (conclusion 16).

By resolution 73/203 of 20 December 2018, the General Assembly took note of the conclusions on identification of customary international law, the text of which was annexed to the resolution, with the commentaries thereto, bought them to the attention of States and all who may be called upon to identify rules of customary international law and encouraged their widest possible dissemination. The General Assembly also acknowledged the utility of published digests and surveys of practice relating to international law, including those that make legislative, executive and judicial practice widely available, and encouraged States to make every effort to support existing publications and libraries specialized in international law.

1 See Yearbook … 2011, vol. II (Part Two), para. 365–367.

2 See ibid., annex I.

3 See Yearbook … 2012, vol. II (Part Two), para. 157.

4 See Yearbook … 2013, vol. II (Part One), document A/CN.4/663.

5 See ibid., document A/CN.4/659.

6 See Yearbook … 2013, vol. II (Part Two), paras. 64–65.

7 See Yearbook … 2014, vol. II (Part Two), paras. 135 and 137.

8 See ibid., para. 136.

9 See Yearbook … 2015, vol. II (Part One), document A/CN.4/682.

10 See Yearbook … 2015, vol. II (Part Two), paras. 58–59.

11 See ibid., para. 60.

12 See ibid., para. 61.

13 Document A/CN.4/695 and Add.1.

14 Document A/CN.4/691.

15 See Yearbook … 2016, vol. II (Part Two), para. 54.

16 See ibid., para. 55.

17 See ibid., paras. 57 and 59, 62–63.

18 See ibid., para. 58.

19 See ibid., para. 60.

20 See ibid., paras. 56 and 301.

21 Document A/CN.4/717.

22 Document A/CN.4/717/Add.1.

23 Document A/CN.4/716.

24 Document A/CN.4/710/Rev.1.

25 See Yearbook … 2018, vol. II (Part Two), para. 57.

26 See ibid., paras. 58–66.

27 See ibid., para. 63.