Unlike UN treaty-bodies and regional human rights tribunals, the manner in which States may bring a case before the International Court of Justice (ICJ) is determined by the manner in which they have expressed their consent to be bound by the Court’s decisions. Thus, the ICJ may decide over a dispute only if the States concerned have recognized its jurisdiction through unilateral declarations (also known as ‘compulsory’ jurisdiction), a jurisdictional clause in bilateral or multilateral treaties (‘treaty based’ jurisdiction), or through an agreement among parties accepting to submit a matter to the ICJ in the event of a dispute (‘special agreement’). Likewise, States may also express their desire to enable the ICJ to entertain a case to which they are parties after it has been seized to adjudicate on the matter (forum prorogatum rule).
Notwithstanding this unique framework, recognizing the jurisdiction of the ICJ in any such form is accompanied by a duty to cooperate with its contentious proceedings. In a broad sense, such duty is grounded on the good faith principle governing international legal commitments, which, as described by the ICJ in the Nuclear Tests Case, entitles States ‘to require that the obligation thus created be respected.’ Even though States’ cooperation is essential for the proper conduct of proceedings before the ICJ (particularly in elucidating the facts of the case), such duty is not explicitly provided for in the Statue of the ICJ, which is limited to regulating the procedural implications arising in the event of default by one party.
Authors such as Kolb argue that the absence of sanctions under Article 53 of the ICJ Statute should by no means be interpreted as preventing the existence of States’ obligation to appear before the Court, since ‘[i]t is an elementary legal conclusion that the absence of a specific sanction does not affect the legal obligation to which such sanction would relate.’ Von Magoldt and Zimmermann, on the other hand, argue that no such obligation to appear can be inferred from the text of the ICJ Statute. Rather, following the rationale of the ICJ in the case concerning the Paramilitary Activities in and against Nicaragua (the Nicaragua Case), they suggest that Article 53 is designed to guarantee the equality of the parties by allowing the procedure to continue unhindered despite lack of cooperation and by ‘affording the defaulting party until the very last minute the possibility to present its case.’
Be it as it may, it is undisputed that non-cooperation with proceedings before the ICJ threatens the proper administration of justice and may produce procedural disadvantages for the absent party. Indeed, as recently asserted by the ICJ in the case of Guyana v. Venezuela, ‘the non-appearing party forfeits the opportunity to submit evidence and arguments in support of its own case and to counter the allegations of its opponent. For this reason, the Court does not have the assistance it might have derived from this information.’ This does not mean, however, that the ICJ must automatically decide in favour of the appearing party when the other is in default, nor does it imply that the non-cooperating State stops being a party for purposes of the proceedings. Moreover, even when the procedure is allowed to move forward without the in presentia participation of one of the parties, the resulting judgment has full res judicata effects and binds both of them irrespective of their degree of cooperation.
While a duty to cooperate with the contentious proceedings brought before the ICJ has not been explicitly established in the constituting documents or jurisprudence of the Court, the same is not true for States’ obligation to abide by its judgments. This notion is explicitly provided in Article 94 of the Charter of the United Nations (UN Charter), which affirms that ‘[e]ach Member of the United Nations undertakes to comply with the decision of the International Court of Justice in any case to which it is a party.’ Moreover, such provision must be interpreted in the light of the ICJ Statute, which assigns binding force to the decisions rendered by the Court (Article 59) and describes their unchallengeable, rex judicata effects (Article 60). The ICJ Statue is silent, however, on the means by which Sates are to implement its decisions or report on their compliance. Likewise, although a favourable decision may recognize a party’s right to claim performance from the other, the exercise of such prerogative is fully subject to the claimant’s will. Indeed, given that the ICJ acts as a subsidiary mechanism for dispute resolution, the parties remain free to settle the matter on different terms than those specified in a judgment and to renounce to any claims to which they are entitled by virtue of it.
A different situation may arise from a State Party’s outright refusal to implement a judgment by the ICJ. Article 94(2) allows the UN Security Council to ‘make recommendations or decide upon measures to be taken to give effect to the judgment’ in the event of non-compliance by one of the parties to a dispute. Although there have been a number of instances in which States request the Security Council to enforce ICJ judgments, it has never made use of such power in practice. As a political body, however, this course of action would be highly contingent on the will of the Security Council’s five permanent members, which can block enforcement through their veto powers when their interests are at stake.
Two precedents are particularly illustrative of this issue. The first is in the context of the Nicaragua Case, where the United States blocked a Security Council resolution that would have required it to comply with an ICJ judgment that had found it in violation of the prohibition on the use of force. The second is related to the judgment in the Avena Case, where Mexico submitted a letter to the Security Council denouncing the lack of compliance of the United States with the ICJ’s order not to execute 51 Mexican nationals. The Security Council did not take any action on the matter, but Mexico did not insist, seemingly aware of the fact that, as Brown describes it, such a request ‘[would] be meaningless if it is directed against a permanent member of the Security Council, or against the interests of a permanent member.’
It should be noted, however, that States have implemented judgments rendered by the ICJ in the majority of cases. Non-compliance remains rare and can be attenuated by a number of factors (such as practical or financial constraints) that are not always indicative of a State’s negative intentions. Moreover, many cases are resolved amicably before a final judgment is reached and, therefore, overall cooperation with the ICJ should be assessed in connection to the pacifying effects of its dispute-settlement mechanisms.
 Rules of Court (Adopted 14 April 1978, entered into force 1 July 1978) arts 34-36, as amended; Swiss Federal Department of Foreign Affairs, Handbook on Accepting the Jurisdiction of the International Court of Justice: Model Clauses and Templates (2014) para 7.
 Statute of the International Court of Justice (18 April 1946) art 36(2); Swiss Federal Department of Foreign Affairs (n 1) paras 21-24.
 Statute of the International Court of Justice (18 April 1946) art 36(1); Swiss Federal Department of Foreign Affairs (n 1) paras 39-43.
 Statute of the International Court of Justice (18 April 1946) art 36(1); Swiss Federal Department of Foreign Affairs (n 1) paras 68-70.
 Rules of Court (n 1) art 38(5); Swiss Federal Department of Foreign Affairs (n 1) paras 91-93.
 Robert Kolb, The International Court of Justice (Hart Publishing 2013) 678.
 ICJ, Nuclear Tests (Australia v France) (Judgment)  ICJ Rep 253 para 46.
 Robert Kolb, The Elgar Companion to the International Court of Justice (Edward Elgar Publishing 2014) 249-250.
 ICJ Statute art 53.
 Kolb (n 6) 692.
 Hans von Mangoldt and Andreas Zimmermann, ‘Article 53’ in Andreas Zimmermann and Christian J Tams (eds), The Statute of the International Court of Justice: A Commentary (3rd edn, OUP 2019) 1469; See also Torsten Stirner, The Procedural Law Governing Facts and Evidence in International Human Rights Proceedings (Brill | Nijhoff 2021) 387-390.
 See ICJ, Case Concerning the Paramilitary Activities in and Against Nicaragua (Nicaragua v United States of America)  (Judgment) ICJ Rep 14, para 59: ‘The Court is careful, even where both parties appear, to give each of them the same opportunities and chances to produce their evidence; when the situation is complicated by the non-appearance of one of them, then a fortiori the Court regards it as essential to guarantee as perfect equality as possible between the parties. Article 53 of the Statute therefore obliges the Court to employ whatever means and resources may enable it to satisfy itself whether the submission of the applicant Sate are well-founded in fact and law, and simultaneously to safeguard the essential principles of sound administration of justice.’
 ibid 1493-1494.
 Kolb (n 6) 690-693; Stirner (n 11) 387.
 ICJ, Arbitral Award of 3 October 1899 (Guyana v Venezuela)  (Judgment) General List No 171 para 25. This reasoning can also be found in the previous cases of Nuclear Tests (n 7) para 15, Nicaragua v United States of America (n 154) para 27, and Fisheries Jurisdiction (Federal Republic of Germany v Iceland)  (Judgment) ICJ Rep 49 para 13.
 Guyana v Venezuela (n 16) para 27; Nicaragua v United States of America (n 12) para 28; See also von Mangoldt and Andreas Zimmermann (n 11) 1487.
 ICJ Statute art 50; Guyana v Venezuela (n 16) para 26; Nicaragua v United States of America (n 12) para 28.
 Nicaragua v United States of America (n 12) para 28
 United Nations, Charter of the United Nations (Adopted 26 June 1945, entered into force 24 October 1945) 1 UNTS XVI, art 94(1).
 ICJ Statute arts 59-60; For an explication on the scope of the res judicata principle, see Case Concerning the Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v Serbia and Montenegro)  (Judgment) ICJ Rep 3, para 115; See also Chester Brown, ‘Article 59’ in Andreas Zimmermann and Christian J Tams (eds), The Statute of the International Court of Justice: A Commentary (3rd edn, OUP 2019) 1571-1572.
 Kolb (n 8) 85.
 See Continental Shelf (Tunisia/Libyan Arab Jamahiriya)  (Judgment) ICJ Rep 18, para 118.
 Kolb (n 8) 85.
 UN Charter art 94(2).
 UN Security Council, ‘The Rule of Law: Can the Security Council Make Better Use of the International Court of Justice?’(2016) Research Report 5-6.
 ibid 6; Kolb (n 8) 65; Brown (n 20) 1586.
 UN Security Council (n 25) 6.
 Brown (n 20) 1586
 Kolb (n 8) 65.