Intervention before the ICJ: A practical guide

30 September, 2022

Written by Sean Aughey & Amy Sander

A. Introduction

1. This article explains the options available to States for intervening in a contentious case before the International Court of Justice (‘the ICJ’). We outline (i) the procedural mechanics (ie, what to do and when) and (ii) the key strategic considerations (ie, whether and how to act).

2. Whilst there have been few interventions, with the majority of rare attempts rejected by the Court, recent developments have brought the issue to the fore. Most notably, at the time of writing, 15 States (Latvia, Lithuania, New Zealand, the UK, Germany, USA, Sweden, Romania, France, Poland, Italy, Denmark, Ireland, Finland and Estonia) have filed declarations to intervene in the Ukraine v Russia (Genocide Convention) case and 4 States(the Netherlands, Canada, the Maldives and the UK) have announced an intention to  intervene in Gambia v Myanmar.

B. The two avenues for intervention

1. The Statute of the ICJ provides two avenues for a State to intervene in a case.

2. The first avenue is an application for permission to intervene under Article 62 of the Statute. This Article provides in subparagraph (1) that: “Should a State consider that it has an interest of a legal nature which may be affected by the decision in the case, it may submit a request to the Court to be permitted to intervene”. Subparagraph (2) provides that: “It shall be for the Court to decide upon this request.” The ICJ has stated that it will determine the admissibility of the request by reference to the conditions in Article 62, but it has no general discretion to grantor reject a request for reasons simply of policy (Territorial and Maritime Dispute (2011), para.36). In practice, however, given the lack of clarity over the conditions under Article 62, the Court retains a large measure of discretion. While not apparent from the text of Article 62,the Court has plotted a fork in this avenue, distinguishing between intervention as a nonparty and as a party.

3. Applications to intervene under Article 62 are rare. Applications under Article 62 have been made in only 11 cases (ie, in around 8% of cases) by a total of 14 States. Only 3 of those applications were granted: Nicaragua in Land, Island and Maritime Frontier Dispute(1990), Equatorial Guinea in Land and Maritime Boundary between Cameroon and Nigeria (1999),and Greece in Jurisdictional Immunities (2011).

4. The second avenue is the right to intervene under Article 63 of the Statute, which provides in subparagraph (1) that: “Whenever the construction of a convention to which states other than those2concerned in the case are parties is in question, the Registrar shall notify all such states forth with”. Subparagraph (2) explains that: “Every state so notified has the right to intervene in the proceedings; but if it uses this right, the construction given by the judgment will be equally binding upon it.” The Rules of Court clarify that a State wishing to avail itself of the right under Article 62 must file a declaration to that effect (Rules of Court, Article 82(1)), and that a State that considers itself a party to the relevant convention may file a declaration even if it has not received a relevant notification from the Registrar (Rules of Court, Article 82(3)).

5. Historically, attempts to intervene under Article 63 are even rarer. Declarations have been filed in just 4 cases (ie, in around 3% of cases) by a total of just 7 States. Only 2 of those declarations were found admissible: Cuba in Haya de la Torre (1951) and New Zealand in Whaling in the Antarctic (2013).

6. Contracting States to the Court’s Statute have thereby consented in advance to the Court’s competence to rule on and admit interventions under Article 62 and Article 63 in cases to which they are a party (Land, Island and Maritime Frontier Dispute (1990), para 96). In the context of Article 62, the Court has observed that opposition by the parties to an application to intervene “though very important” is “no more than one element to be taken into account”: Land, Island and Maritime Frontier Dispute (1990), para. 96.

7. Distinct from intervention, and potentially as a prior step (as in Haya de la Torre (1951), p.74), a State also has the option to request to be provided with copies of the pleadings and documents in a given case (Rules of Court, Article 53(1)). At the discretion of the Court, such request may be granted or, as with the request of Netherlands and Canada in the Gambia v Myanmar case, rejected (Gambia v Myanmar (2022), para. 15).

C. Procedure: what to do and when

8. A State intending to make use of either avenue for intervention must be mindful of timing and the stage of the relevant proceedings before the Court.

a. The intervention “shall” be made “as soon as possible” (Rules of Court, Article 81(1)and 82(1)), with the Court in the Pulau Ligitan case emphasising this is “essential for an orderly and expeditious progress of the procedure before the Court” (Pulau Ligitan (2002), para.21).

b. With respect to Article 62, an application for permission to intervene must be made “not later than the closure of the written proceedings” (Rules of Court, Article 81(1)). With respect to Article 63, the relevant declaration must be filed “not later than the date fixed for the opening of the oral proceedings”, without specifying that this relates to the merits(Rules of Court, Article 82(1)). A prospective intervener must keep a close eye on the schedule fixed by the Court. Whereas hearings will be publicly announced in advance, it can be difficult to anticipate exactly when the written proceedings will close since the procedural timetable is subject to amendment including by agreement3of the parties. States wishing to intervene under Article 62 should therefore prepare their application in good time.

c. An application/declaration submitted at a later stage “may” be admitted, but only where the Court is satisfied that there are relevant “exceptional circumstances”, a notably vague and seemingly high bar to satisfy which the Court has not yet expanded upon(Rules of Court, Article 81(1) and 82(1)).

9. The content of the filing is set out in the Rules of Court and, as with any written document presented to the Court, this is best presented in succinct and clear terms. For any intervention the filing must state the name of an agent, specify the case to which it relates, and include a list of documents in support with those documents attached (Rules of Court, Article 81(2) and 82(2)). The further information to be provided varies depending on which avenue for intervention is being followed:

a. Article 62: An application must set out: (a) the interest of a legal nature which the State applying to intervene considers may be affected by the decision in that case;(b) the precise object of the intervention; and (c) any basis of jurisdiction which is claimed to exist as between the State applying to intervene and the parties to the case(although the Court has since clarified that (c) is not required if the State wishes to intervene as a non-party: Territorial and Maritime Dispute (2011), para. 28). There is no requirement that the intervening State has entered into prior negotiations with one/both parties to the case with respect to a defined dispute: Land, Island and Maritime Frontier Dispute (1990), para 51.

b. Article 63: A declaration must: (a) set out the particulars of the basis on which the declarant State considers itself a party to the convention; (b) identify the particular provisions of the convention the construction of which it considers to be in question; and (c) include a statement of the construction of those provisions for which it contends.

10. Following a filing under Article 62 or Article 63, the subsequent stages in the procedure are as follows:

a. Transmission of copies of the filing: The relevant application/declaration is communicated by the Registrar of the ICJ to the parties in the case and also to (a) the Secretary General of the United Nations; (b) the Members of the United Nations; (c) other States entitled to appear before the Court; and (d) any other States which have been notified under Article 63 of the Statute (Rules of Court, Article 83).

b. Written response of the parties to the case: The parties to the relevant case are then invited to set out their observations in writing, within a time limit to be fixed by the Court or by the President if the Court is not sitting (Rules of Court, Article 83).

c. Hearing in event of an objection by either or both of the parties to the case: If either or both of the parties file an objection to the application for permission to intervene, or to the admissibility of a declaration of intervention, the Court must hear the State seeking to intervene and the parties before deciding (Rules of Court, Article 84(2)). Judges ad hoc appointed by the parties are entitled to sit, but the State seeking to intervene is not entitled to appoint its own judge ad hoc having “yet to establish any status in relation to the case” (Tunisia/Libya Continental Shelf (1981), para. 8).

d. Decision of the Court: The Court will then decide whether an application for permission to intervene under Article 62 of the Statute should be granted, and whether an intervention under Article 63 of the Statute is admissible, “as a matter of priority unless in view of the circumstances of the case the Court shall otherwise determine” (Rules of Court, Article 84 (1)).

e. Written pleadings: If the Court finds in favour of the intervening State, that State will be provided with copies of the pleadings and documents, and time limits will be set for its submission of a “written statement” with respect to Article 62 (Rules of Court, Article 85), or “written observations” with respect to Article 63 (Rules of Court, Article86).

f. Judge ad hoc: A State intervening as a non-party (whether under Article 62 or Article63) has no entitlement to appoint a judge ad hoc (Whaling in the Antarctic (2013), para18, addressing Article 63 but identifying a statement of principle also applicable to Article 62). A State intervening as a party under Article 62 is entitled to appoint a judge ad hoc (Article 31, Statute) unless there is already a member of the Court of the nationality of any one of the parties “in the same interest” (Statute, Article 31(5) and Rules of Court, 36(1)), a scenario which the Court has not yet had to consider (Cf. Whaling in the Antarctic (2013), para 21).

g. Oral pleadings: The intervening State will be entitled to make oral submissions on the subject-matter of the intervention (Rules of Court, Article 85(3), Article 86(2)).Although there is no set procedure, the Court’s most recent practice appears to indicate a preference for the State intervening under either avenue to be given one round of oral pleadings after the first round of the parties: in Jurisdictional Immunities, Greece had one round of two hours; in Whaling in the Antarctic, New Zealand hadone round of 1.5 hours.

D. Strategy: whether and how to act

What are the prospects of success?

11. Article 63: If the construction of a convention to which the intervening State is party is in question, Article 63 provides the advantage that this is the only ‘box to be ticked’, and the State has the right to then intervene. The other side to this seemingly shiny coin is that the intervening State must then accept the Court’s judgment on the point of construction as binding upon it. Given the wider practical significance, in any event, of the Court’s determination on the construction of a multilateral convention for all contracting States to that convention, the fact that its construction is not strictly legally binding on non intervening States may be of limited comfort to them.

12. A further strategic question concerns the timing of a declaration. While Article 82(1) of the Rules of Court leaves the question open, and questions of the construction of a provision of a multilateral convention often arise at the jurisdiction stage (most obviously in relation to the scope of a dispute settlement clause), the Court has not yet ruled on an attempt to intervene specifically and only on such basis at the jurisdiction stage (Cf Military and Paramilitary Activities in and against Nicaragua (1984), para. 2, where the Court’s rejected El Salvador’s attempt to intervene at the jurisdiction stage, finding that its declaration also addressed matters of construction that “presuppose that the Court had jurisdiction to entertain the dispute”). This question now arises in relation to the multiple declarations that have been filed at the jurisdiction stage in the Ukraine v Russia (Genocide Convention) case.

13. Article 62: To proceed under Article 62, the intervening State arguably has more of an uphill struggle and at the very least must factor for an unpredictability of outcome given the ambiguous thresholds and lack of precedent and clear guidance. The intervening State must establish that (i) it has “an interest of a legal nature” and that (ii) this interest is one “which may be affected by the decision in the case” (i.e. that the interest may (not will or must) be affected in its content and scope by either the dispositif or the reasons which constitute the necessary steps to the dispositif: Territorial and Maritime Dispute (2011), paras. 37 and 38). These are inherently general conditions, which the Court itself has recognised can only be assessed “in concreto and in relation to all the circumstances of a particular case” (Land, Island and Maritime Frontier Dispute (1990), para. 61).

14. The Court has laid down markers that a presentation of high level considerations will not pass muster: mere interest “in the general legal rules and principles likely to be applied by the decision” is insufficient (Land, Island and Maritime Frontier Dispute (1990), para 76), and the interest “has to be the object of a real and concrete claim of that State, based on law, as opposed to a claim of a purely political, economic or strategic nature” (Territorial and Maritime Dispute (2011), para 37). Some commentators have suggested that reliance on an obligation erga omnes may be sufficient. The Court has not ruled on this issue in a given case, and the uncertainty is highlighted by the change of tack of Greece from a general legal interest in the scope and meaning of State immunity under customary international law as a basis for intervention to a more honed particularisation of its legal interest (Jurisdictional Immunities (2011), paras. 19-20).

If Article 62, to intervene as a party or non-party?

15. A further strategic decision to be made with respect to Article 62 is whether to intervene as a party or non-party. In the former case, a basis of jurisdiction as between the State seeking to intervene and the parties to the main proceedings is required, and the intervening State is bound by the Court’s judgment, whereas in the latter, that judgment has effect only between the parties to the main proceedings, pursuant to Article 59 of the Statute (Territorial and Maritime Dispute (2011), para 23).

16. The Court has said that if seeking to intervene as a non-party, that State does not have to establish that one of its rights (as opposed to interests of a legal nature) may be affected but it should, at the same time, advance “a real and concrete claim … based on law” (Territorial and Maritime Dispute (2011), para 37). Quite how this distinction might apply in practice to the facts of a given case will require careful consideration. In framing its interests of a legal nature, including the articulation of any real and concrete legal claim, the State seeking to intervene must be wary of the need to avoid introducing a new dispute by inviting the Court to pronounce on the existence or scope of its own rights and obligations or those of other non-parties (see Territorial and Maritime Dispute (2011), para 44; Land, Island and Maritime Frontier Dispute (1990), para 98).

What is the State’s ultimate (and long-term) objective(s)?

17. In any given case, careful reflection will be needed in order to identify the State’s objective(s) (both short-term and long-term) and to assess whether and how that objective(s) can be best achieved by intervening in the relevant contentious case before the Court. While the individual circumstances of the case will be key to this assessment, the State’s objectives may extend far broader and relate, for example, to supporting other States (including one of the parties), facilitating the peaceful resolution of the underlying dispute between the parties, consolidating opinio juris on a particular issue of customary international law, and/or maintaining the authority of the Court and the willingness of States to submit their disputes to the Court. The Court is also likely to have in mind at least some of these objectives (Cf. eg Military and Paramilitary Activities in and against Nicaragua, Dissenting Opinion Judge Schwebel, 231: “If the Court is to deserve and maintain the confidence of States, it must act with scrupulous regard to the letter and spirit of the Rules”).


This note is provided free of charge as a matter of information only by its author. It is not intended to constitute, nor should it be relied upon as constituting, legal advice, and no responsibility is assumed (whether by its author or any of the other self-employed members of Essex Court Chambers) in relation to the accuracy of the contents of the same as regards anyone choosing to rely upon it.