1 Customary International Humanitarian LAW (Jean-Marie, Henckaerts & Louise, Doswald-Beck eds., 2 vols. 2005)Google Scholar; see also Jean-Marie, Henckaerts, Study on Customary International Humanitarian Law: A Contribution to the Understanding and Respect for the Rule of Law in Armed Conflict, Int’l Rev. Red Cross, No. 857, Mar. 2005, at 175 Google Scholar (providing an overview of the study’s purpose, methodology, and findings).

2 See, e.g., Dunbar, N. C. H., The Myth of Customary International Law, 1983 Austl.Y.B. Int’l L. 1 Google Scholar; Estreicher, Samuel, Rethinking the Binding Effect of Customary International Law, 44 Va. J. Int’l L. 5, 14–15 (2003).Google Scholar

3 In this essay, I will leave aside debates, developed extensively in other scholarship, as to whether the “modern” approach to discerning customary international law is likely to strengthen the ability of the international legal system to respond effectively to contemporary problems. See, e.g., Restatement (Third) of the Foreign Relations Law of the United States §102 reporters’ note 2 (1987); Anthea Elizabeth, Roberts, Traditional and Modern Approaches to Customary International Law: A Reconciliation, 95 AJIL 757, 758–59 (2001).Google Scholar This development has been criticized by some. See, e.g., J Kelly, Patrick, The Twilight of Customary International Law, 40 Va. J. Int’l L. 449 (2000)Google Scholar (criticizing customary international law in part on the basis of the lack of serious, inductive assessment of state practice and opinio juris).

4 See George, H. Aldrich, The Jurisprudence of the Iran-United States Claims Tribunal 218 (1996).Google Scholar

5 See, e.g., Antonio R. Parra, Applicable Substantive Law in ICSID Arbitrations Initiated Under Investment Treaties, paper delivered at Seventeenth Joint International Centre for Settlement of Investment Disputes (ICSID) /American Arbitration Association/ICC Court Colloquium (Nov. 10,2000), at <http://www.idlo.int/texts/%5C%5CIDLI%5C%5Cmis5850.pdf>.

6 The ILC’s Articles on Responsibility of States for Internationally Wrongful Acts, adopted under the leadership of James Crawford, will no doubt inform disputes concerning state responsibility, but resort to primary sources will still be necessary. Articles on Responsibility of States for Internationally Wrongful Acts, in Report of the International Law Commission on the Work of Its Fifty-third Session, UN GAOR, 56th Sess., Supp. No. 10, at 43, UN Doc. A/56/10 (2001), reprinted in Crawford, James, The International Law Commission’s Articles on State Responsibility: Introduction, Text and Commentaries 65 (2002), available at <http://www.un.org/law/ilc>>Google Scholar.

7 Detlev, F. Vagts, International Relations Looks at Customary Law: A Traditionalist Defense, 15 Eur. J. Int’l L. 1031, 1036 (2004).Google Scholar There has been an effort to codify the law of sovereign immunity in the UN Convention on Jurisdictional Immunities of States and Their Property, GA Res. 59/508, annex (Dec. 2, 2004), opened for signature Jan. 17, 2005, 44 ILM 803 (2005). However, as the treaty is not yet in effect and ratification prospects are uncertain, customary law remains for now the governing law.

8 On May 28, 2004, the International Law Commission approved on first reading the draft articles proposed bv John Dugard. See Fifth Report on Diplomatic Protection, UN Doc. A/CN.4/538 (2004).

9 See Partial Award of Eritrea’s Civilian Claims, 44 ILM 601, paras. 28, 30 (2005) (Eri.-Eth. CI. Comm’n Dec. 17, 2004) [hereinafter Partial Award].

10 Meron, Theodor, The Implications of The European Convention on Human Rights For the Development of Public International Law (2000)Google Scholar; Caflisch, Lucius & Antônio A., Cançadp Trindade, Les Conventions américaine et européenne des Droits de l’Homme et le droit international général, 108 Revue Général De Droit International Publique 5 (2004).Google Scholar

11 Velásquez Rodríguez v. Honduras, Inter-Am. Ct. H.R. (ser. C) No. 4, paras. 164-65, 172 (1988).

12 Garrido and Baigorria v. Argentina, Inter-Am. Ct. H.R. (ser. C) No. 39, paras. 40, 68-74 (1998).

13 Assanidze v. Georgia, 2004-11 Eur. Ct. H.R., paras. 144-50 (2004).

14 Ilaşcu v. Moldova, App. No. 48787/99, paras. 441-42, 455-64 (Eur. Ct. H.R. 2004), available at <http://www.echr.coe.int>.

15 Al-Adsani v. United Kingdom, 2001-XI Eur. Ct. H.R., paras. 30, 60 (2001), reprinted in 123 ILR 24.

16 North Sea Continental Shelf (FRG/Den.; FRG/Neth.), 1969 ICJ Rep. 3, paras. 73-81 (Feb. 29).

17 Military and Paramilitary Activities in and Against Nicaragua (Nicar. v. U.S.), Merits, 1986 ICJ Rep. 14, para. 177 (June 27) [hereinafter Nicaragua].

18 Id., paras. 218-20.

19 For instance, the Eritrea-Ethiopia Claims Commission has treated the Geneva Conventions as presumptively reflective of customary international law, which places the burden of proof on the party claiming that any given provision is not customary law. Partial Award, supra note 9, at B2, 44 ILM at 626.

20 Meron, Theodor, Human Rights and Humanitarian Law as Customary Law 25–62 (1989)Google Scholar [hereinafter Meron, Human Rights]; Meron, Theodor, The Geneva Conventions as Customary Law, 81 AJIL 348, 360 (1987).Google Scholar

21 Meron, Human Rights, supra note 20, at 25-62.

22 Nicaragua, supra note 17, paras. 187-93.

23 Id., paras. 194-201.

24 Id., paras. 202-09.

25 Arrest Warrant of 11 April 2000 (Dem. Rep. Congo v. Belg.), 2002 ICJ Rep. 3, para. 52 (Feb. 14).

26 Id., para. 58.

27 Id., Dissenting Opinion of Judge Van den Wyngaert, para. 12; see also id., Joint Separate Opinion of Judges Higgins, Kooijmans, and Buergenthal.

28 See, e.g., Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territories, Advisory- Opinion, 43 ILM 1009 (Int’l Ct. Justice July 9, 2004) (applying several customary international law principles); see also id., Declaration of Judge Buergenthal, para. 7 (concerning the failure to address certain facts or evidence); Oil Platforms (Iran v. U.S.), 2003 ICJ Rep. 803, para. 42 (Nov. 6) (holding, on the basis of a perfunctory assessment of both custom and evidence, that customary law requires that the right of self-defense be limited by the requirements of necessity and proportionality); id., Separate Opinion of Judge Buergenthal, paras. 33-46 (discussing defective fact-finding process); Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 ICJ Rep. 226, para. 79 (July 8) (declaring the fundamental rules of international humanitarian law to be “intransgressible principles of international customary law”).

29 Nicaragua, supra note 17, para. 186. Of course, states bent on evading compliance with rules of international law commonly resort to factual or legal exceptions or justifications contained in the rule itself. Meron, Human Rights, supra note 20, at 59-60.

30 Report of the Secretary-General Pursuant to Paragraph 2 of Security Council Resolution 808 (1993), UN Doc. S/25704, para. 34 (1993).

31 See Legality of Use of Force (Serb. & Mont. v. Italy), Joint Declaration of Vice-President Ranjeva, Judges Guillaume, Higgins, Kooijmans, Al-Khasawneh, Buergenthal and Elaraby, para. 3 (Int’l Ct. Justice Dec. 15, 2004) (stating that in discerning principles of law, the ICJ “must ensure consistency with its own past case law in order to provide predictability” and that “ [consistency is the essence of judicial reasoning”).

32 Prosecutor v. Delalić, Appeals Judgment, No. IT-96-21-A, para. 179 (Feb. 20, 2001).

33 Prosecutor v. Kordić and Čerkez, Appeals Judgment, No. IT-95-14/2-A, paras. 44-46 (Dec. 17, 2004); see also text at note 104 infra. Nevertheless, in discussing the crimes charged, the appeals chamber satisfied itself of their customary character. Kordić and Čerkez, supra, paras. 48, 52, 54, 59-66.

34 Prosecutor v. Galić, Indictment, No. IT-98-29-I, para. 5 (Mar. 26, 1999).

35 Prosecutor v. Galić, Judgment and Opinion, No. IT-98-29-T (Dec. 5, 2003).

36 See supra note 30 and corresponding text.

37 Prosecutor v. Hadžihasanović, Decision on Command Responsibility, No. IT-01-47-AR72 (July 16, 2003).

38 Id., para. 31.

39 Id., para. 12.

40 Id., para. 13.

41 Id., paras. 14-15.

42 Id., para. 17.

43 327 U.S. 1, 14-15 (1946).

44 Hadžihasanović, Decision on Command Responsibility, supra note 37, para. 27.

45 Prosecutor v. Hadžihasanović, Decision on Joint Challenge to Jurisdiction, No. IT-01-47-PT, paras. 67-93 (Nov. 12, 2002).

46 Prosecutor v. Hadzihasanovic, Third Amended Indictment, No. IT-01-47-PT, para. 6 (Sept. 26, 2003).

47 Id., paras. 39, 40, 44, 45.

48 Hadžihasanović, Decision on Command Responsibility, supra note 37, para. 45.

49 Id., paras. 46-48, 50.

50 Id., para. 51.

51 Id., para. 55. It is not necessary to discuss here whether the principle of legality constitutes a jus cogens norm.

52 Id., Partial Dissenting Opinion of Judge Shahabuddeen, para. 2.

53 Id., Separate and Partially Dissenting Opinion of Judge Hunt.

54 Id., Partial Dissenting Opinion of Judge Shahabuddeen, para. 14. r’s Id., para. 15.

55 Id., para. 15.

56 Hadžihasanović, Decision on Command Responsibility, supra note 37, para. 12 (holding that “where a principle can be shown to have been so established [as custom], it is not an objection to the application of the principle to a particular situation to say that the situation is new if it reasonably falls within the application of the principle”).

57 For a criticism of the Hadžihasanović dissent along somewhat similar lines, see Greenwood, Christopher, Command Responsibility and the Hadžihasanović Decision, 2 J. Int’l Crim. Just. 598 (2004).CrossRefGoogle Scholar

58 Shahabuddeen, Mohamed, Does the Principle of legality Stand in the Way of Progressive Development of Law? 2 J. Int’l Crim. Just. 1007 (2004).CrossRefGoogle Scholar

59 C.R. v. United Kingdom, 335-C Eur. Ct. H.R. (ser. A), para. 34 (1995).

60 Id., para. 42.

61 Id., para. 14 (quoting R. v. R., [1991] 93 Crim. App. R. 1, 8).

62 Id., para. 41.

63 Prosecutor v. Milutinović, Decision on Motion Challenging Jurisdiction, No. IT-99-37-AR72, para. 38 (May 21, 2003) (citing Delatić Appeals Judgment, supra note 32, para. 173; Prosecutor v. Aleksovski, Appeals Judgment, No. IT-95-14/1-A, paras. 122-27 (Mar. 24, 2000)).

64 Id.

65 Id.

66 Aleksovski, supra note 63, para. 123.

67 Id., para. 126.

68 Id., para. 127.

69 Delalić, Appeals Judgment, supra note 32, paras. 158-73.

70 Id., paras. 228-41.

71 Prosecutor v. Vasiljević, No. IT-98-32-T, paras. 196, 201 (Nov. 29, 2002).

72 Id., para. 201; see also Prosecutor v. Blaskić, Appeals Judgment, No. IT-95-14-A, para. 141 (July 29, 2004); Milutinović, supra note 63, para. 9; Guénaël, Mettraux, International Crimes and the ad hoc Tribunals 6–7 (2005)Google Scholar (arguing that a treaty itself, i.e., without being crystallized as customary law, cannot be a basis for a criminal conviction, id. at 9; and criticizing Galić for equating illegality and criminality).

73 Id., para. 203. In Prosecutorv. Stakić, the trial chamber held that the crime against humanity of committing “other inhumane acts” (Article 5(i) of the Statute) lacks sufficient clarity, precision, and definiteness and might violate the principle of nullum crimen. Prosecutor v. Stakić, No. IT-97-24-T, para. 719 (July 31, 2003) (currently on appeal).

74 Vasiljević, supra note 71, para. 203.

75 See, e.g., Prosecutor v. Milutinović, Reasons for Decision Dismissing Interlocutory Appeal, No. IT-99-37-AR- 72.2 (June 8, 2004), 35 ILM 32 (1996).

76 Prosecutor v. Tadić, Interlocutory Appeal on Jurisdiction, No. IT-94-1-AR72, para. 99 (Oct. 2, 1995).

77 Id., paras. 100-25.

78 Id., para. 137.

79 Prosecutor v. Šešelj, Appeal Concerning Jurisdiction, No. IT-03-67-AR72.1, para. 5 (Aug. 31, 2004) (noting, citing previous decisions, that customary international law does not require that crimes against humanity be committed in an armed conflict, but that this requirement was instead imposed by the ICTY Statute).

80 Prosecutor v. Kunarac, Appeals Judgment, No. IT-96-23 & 23/1-A, para. 86 (June 12, 2002) (finding that under customary law, an “attack” can precede, outlast, or continue during an “armed conflict,” but need not itself be part of an armed conflict).

81 E.g., Tadić, Appeals Judgment, No. IT-94-1-A, paras. 287-92 (July 15, 1999) (finding that customary international law does not require that discriminatory or persecutory intent be established for all crimes against humanity); Prosecutor v. Kupreškić, No. IT-95-16, para. 558 (Jan. 14, 2000) (following Tadić and holding that discriminatory intent is required only with regard to the category of “persecutions” under Article 5(h)).

82 E.g., Kunarac, supra note 80, para. 98 & n.114 (holding, based on the “overwhelming[]” consensus of relevant state practice—including judicial precedents of Canada, Australia, Israel, the Federal Republic of Yugoslavia (Kosovo), and the Nuremberg Tribunal, as well as reports of the secretary-general and the International Law Commission— that crimes against humanity need not be undertaken pursuant to a policy or plan).

83 Tadić, Appeals Judgment, supra note 81, paras. 255-70 (holding, based principally on an evaluation of case law of various countries pertaining to the Holocaust, that under customary law, ‘“purely personal motives’ do not acquire any relevance for establishing whether or not a crime against humanity has been perpetrated”; id. at 270).

84 Blaškić, supra note 72, paras. 143,147-49,152,156-59 (finding, inter alia, that an inherent right to life, as well as prohibitions against pillage, deportation, and forcible transfer, have customary international law status).

85 Prosecutor v. Krstić, Appeals Judgment, No. IT-98-33-A, para. 25 (Apr. 19, 2004) (finding that, according to customary international law, the trial chamber was correct to limit the definition of genocide to acts seeking the physical or biological destruction of all or part of the group).

86 Id., paras. 135-44.

87 Blaškić, supra note 72, paras. 109-16.

88 Kunarac, supra note 80, paras. 145-48 (addressing the extent to which the Convention Against Torture reflects customary international law).

89 See, e.g., Prosecutor v. Erdemović, Appeals Judgment, Joint Separate Opinion of Judge McDonald and Judge Vohrah, No. IT-96-22-A, para. 55 (Oct. 7, 1997) (finding that customary international law does not establish whether duress is a defense to a charge of killing innocent human beings).

90 Prosecutor v. Simić, Decision on Testimony of a Witness, No. IT-95-9-PT, para. 74 (July 27, 1999) (holding that, under customary law, no question of a balance of interest arises between a confidentiality interest and a claim to nondisclosure of the information).

91 Blaskić, Appeals Judgment on Request for Review, No. IT-95-14-108 bis, paras. 38-60 (Oct. 29,1997) (finding that, under customary law, state officials cannot suffer the consequences of wrongful acts that are not attributable to them personally but to the state on whose behalf they act, and that subpoenas therefore cannot be issued to state officials acting in their official capacity).

92 Id., paras. 61-66 (concluding that the drafters of Article 29 of the ICTY Statute departed from international customary law as regards national security concerns because to grant states blanket ability to withhold documents for national security reasons would undermine the essential purpose of the International Tribunal).

93 Prosecutor v. Nikolić, Appeals Decision on Legality of Arrest, No. IT-94-2-AR73, paras. 20-24 (June 5, 2003) (examining domestic case law and concluding that in cases involving universally condemned offenses like genocide and war crimes, jurisdiction should not be set aside even if there were irregularities in the way the accused was brought before the Tribunal).

94 See generally Allison Marston, Danner & Jenny, S. Martinez, Guilty Associations: Joint Criminal Enterprise, Command Responsibility, and the Development of International Criminal Law, 93 Cal. L. Rev. 77 (2005)Google Scholar; Powles, Stephen, Joint Criminal Enterprise, 2 J. Int’l Crim. Just. 606 (2004)CrossRefGoogle Scholar. On crimes of accomplices, see Tadic, supra note 81, para. 220 (holding that the notion of common design as a form of accomplice liability is firmly established in customary international law).

95 Meron, Human Rights, supra note 20, at 41-62.

96 Meron, Theodor, International Criminalization of Internal Atrocities, 89 AJIL 554, 564 (1995).Google Scholar

97 1 Trial of the Major War Criminals Before the International Military Tribunal, Nuremberg, 14 November 1945-1 October 1946, at 218 (1947).

98 Id. at 221.

99 United States v. List, 11 Trials of War Criminals Before The Nuernberg Military Tribunals Under Control Council Law NO. 10, at 759, 1239 (1948).

100 Hans-Heinrich, Jescheck, The General Principles of International Criminal Law Set out in Nuremberg, as Mirrored in the ICC Statute, 2 J. Int’l Crim.Just. 38, 40–42 (2004).Google Scholar

101 Meron, Human Rights, supra note 20, at 37-41.

102 Meron, supra note 96, at 564-67 (arguing that the Nuremberg precedent illustrates the legitimacy of international criminal justice for the Rwandan genocide).

103 Meron, Theodor, War Crimes in Yugoslavia and the Development of International Law, 88 AJIL 78, 84–85 (1994)Google Scholar; Meron, Theodor, From Nuremberg to The Hague, 110 Mil. L. Rev. 107, 111 (1995).Google Scholar

104 Tadić, Interlocutory Appeal on Jurisdiction, supra note 76, paras. 94, 143.

105 See text at note 30 supra.

106 Tadić, Interlocutory Appeal on Jurisdiction, supra note 76, para. 143.

107 Jescheck, supra note 100, at 41.

108 Report of the Secretary-General Pursuant to Paragraph 5 of Security Council Resolution 955 (1994), UN Doc. S/1995/134, paras. 11-12.

109 E.g., Prosecutor v. Akayesu, No. ICTR-96-4-T, paras. 610, 617 (Sept. 2, 1998) (addressing the customary status of Article 4(2) of Additional Protocol II to the Geneva Conventions).

110 Prosecutor v. Kallon, Constitutionality and Jurisdiction, No. SCSL-2004-15-AR72(E), para. 41 (Mar. 13, 2004).

111 Prosecutor v. Fofana, Decision on Jurisdiction Materiae, No. SCSL-2004-14-AR72(E), paras. 21-24 (Ma)’ 25, 2004).

112 Prosecutor v. Kondewa, Jurisdiction/Abuse of Process, No. SCSL-2004-14-AR72(E), paras. 52, 57 (May 25, 2004); Prosecutor v. Gbao, Invalidity of Agreement, No. SCSL-2004-15-AR72(E), paras. 6-10 (May 25, 2004).

113 Prosecutor v. Taylor, Immunity from Jurisdiction, No. SCSL-2003-01-I, paras. 43-53 (May 31, 2004). For the Yerodia case, see supra note 25.

114 Prosecutor v. Norman, Lack of Jurisdiction, No. SCSL-2004-14-AR72(E), paras. 18-24 (May 31, 2004).

115 Rome Statute of the International Criminal Court, July 17, 1998, Art. 21, 2187 UNTS 3.

116 Henckaerts, supra note 1, at 177-78.

117 Meron, Theodor, Towards a Humanitarian Declaration on Internal Strife, 78 AJIL 859 (1984)CrossRefGoogle Scholar; Meron, Theodor, On the Inadequate Reach of Humanitarian and Human Rights Law and the Need for a New Instrument, 77 AJIL 589 (1983).Google Scholar

118 Baxter explained that as the number of states that have ratified a treaty increases, much greater weight is placed, in discerning custom, on the practices of those relatively few states that have not ratified the treaty. See Richard, R. Baxter, Treaties and Custom, 129 Recueil Des Cours 27, 64 (1970 I).Google Scholar For a discussion of the Baxter paradox, see Meron, Human Rights, supra note 20, at 50-51. For methods of deriving customary law evidence from the position of state parties, see id. at 51-57.

119 Henckaerts, supra note 1, at 184.

120 Id.

121 Prosecutor v. Hadžihasanović, Appeal of Decision on Acquittal, No. IT-01-47-AR73.3, paras. 29-30 (Mar. 11, 2005).

122 Prosecutor v. Kordić and Ĉerkez, Motion to Dismiss for Lack of Jurisdiction, No. IT-95-14/2-PT, paras. 15-31 (Mar. 2, 1999).

123 Prosecutor v. Strugar, Decision on Jurisdiction, No. IT-01-42-PT, para. 17 (June 7, 2002).

124 Strugar, Interlocutory Appeal, No. IT-01-42-AR72, paras. 9-14 (Nov. 22, 2002).