1. Art. 38 of the Statute of the International Court of Justice, which is generally considered to state all sources of international law, provides that the ICJ shall apply international conventions, international custom, general principles of law, and (subject to provisions of Art. 59 of the Statute) judicial decisions and doctrine as subsidiary means of interpretation.

2. Meron talks in this regard of the ‘revival of customary law’ for a number of reasons, one of which is the use of customary international law as a primary source by the ICJ and by international criminal courts while upholding the principle of nullum crimen sine lege. T. Meron, ‘Revival of Customary Humanitarian Law’, (2005) 99(4) AJIL 817.

3. I. Detter, The Concept of International Law (1987).

4. 26th International Conference of the Red Cross and Red Crescent, Geneva, 3–7 December 1995, ‘Res. 1, International Humanitarian Law: From Law to Action: Report on the Follow-up to the International Conference for the Protection of War Victims’, (1996) 310 International Review of the Red Cross 58.

5. (Note that all page references are to volume I unless otherwise stated.) Even the broadly ratified Additional Protocol I (AP I) is obstructed in its effectiveness, since several states that are or have been party to an international armed conflict did not ratify it. Similarly, some states that are or have been involved in a non-international armed conflict did not ratify Additional Protocol II (AP II), leaving the realm of protective treaty law limited to Common Article 3 of the (four) Geneva Conventions.

6. In fact the ever developing practice of the UN Security Council with regard to peacekeeping forces demonstrates that customary law is not only suitable but crucial to enable the Charter to function as a living instrument so that it continues to be an appropriate instrument to address contemporary issues and global threats.

7. E.g. T. Meron, The Humanization of International Law (2006); R. Cryer et al., in R. Cryer (ed.), ‘Symposium: Studies on the Customary Law Study’, 2006 Journal of Conflict & Security Law 11 (2), at 163.

8. J. B. Bellinger and W. J. Haynes, ‘A U.S. Government Response to the International Committee of the Red Cross's Customary International Humanitarian Law Study’, (2007) 46 ILM 514; also available at http://www.defenselink.mil/home/pdf/Customary_International_Humanitiarian_Law.pdf (consulted last July 2007).

9. B. Stern, ‘Custom at the Heart of International Law’, trans. M. Byers and A. Denise, (2001) 11 Duke Journal of Comparative and International Law 89 (first published in Mélanges offerts à Paul Reuter (1981)).

10. Some believe that states leave too much of the customary law arena to the decision-making of the ICRC and NGOs that attempt to bind states by issuing ‘authoritative’ studies and commentaries. States ought to proclaim more what they consider to be customary international law and better provide their opinion on the outcome of such studies. The instigation of such dialogue is in fact one of the aims of the Study.

11. Stern, supra note 9, at 91.

12. Ibid.

13. In accordance with recommendation II of the Intergovernmental Group of Experts for the Protection of War Victims as endorsed by the 26th International Conference of the Red Cross and the Red Crescent, supra note 4.

14. See also J.-M. Henckaerts, ‘Study on Customary International Humanitarian Law: A Contribution to the Understanding and Respect for the Rule of Law in Armed Conflict’, (2005) 87 International Review of the Red Cross 176.

15. The Final Declaration adopted by the International Conference for the Protection of War Victims, September 1993, emphasizes the ‘necessity to make the implementation of humanitarian law more effective’, see (1993) 296 International Review of the Red Cross, at 381.

16. The International Conference for the Protection of War Victims called upon the Swiss government to ‘convene an open-ended intergovernmental group of experts to study practical means of promoting respect for and compliance with that law, and to prepare a report for submission to the states and the next session of the International Conference of the Red Cross and the Red Crescent’. Ibid.

17. These recommendations were adopted in January 1995 during the meeting of the Intergovernmental Groups of Experts for the Protection of War Victims (under the presidency of Lucius Caflisch), Geneva, 23–27 January 1995.

18. Ibid., at 84.

19. The highly qualified academic experts who formed the steering committee were Professors Georges Abi-Saab, Salah El-Din Amer, Ove Bring, Eric David, John Dugard, Florentino Feliciano, Horst Fischer, Françoise Hampson, Theodor Meron, Djamchid Momtaz, Milan Šahović, and Raul Emilio Vinuesa.

20. The Plan of Action was adopted in June 1996 and the research started in October 1996.

21. The researchers who contributed to the collection of materials for the study were identified in nearly 50 states: 9 in Africa, 11 in the Americas, 15 in Asia, 1 in Australia, and 11 in Europe (pp. xlv and Annex I to the introduction, p. xlix).

22. Part I: Georges Abi-Saab (Rapporteur), Jean-Francois Quéguiner (Researcher); Part II: Horst Fischer (Rapporteur), Gregor Schotten and Heike Spieker (Researcher); Part III: Theodor Meron (Rapporteur), Richard Desgagné (Researcher); Part IV: Ove Bring (Rapporteur), Gustaf Lind (Researcher); Part V: Françoise Hampson (Rapporteur), Camille Giffard (Researcher); Part VI: Eric David (Rapporteur), Richard Desgagné (Researcher).

23. Resolutions adopted by the Security Council, General Assembly, and Commissions on Human Rights. Ad hoc investigations conducted by the UN, the work of the International Law Commission, work of UN General Assembly Committees, reports of the Secretary-General, thematic and country-specific procedures of the UN Commission on Human Rights, reporting procedures before the Human Rights Committee, the Committee against Torture, the Committee on the Elimination of Discrimination against Women, and the Committee on the Rights of the Child (p. xlvii).

24. As far as possible the included materials run up to 31 December 2002 and are in limited instances of a more recent date (p. xlvi).

25. The drafting of the six different parts and the overall management and supervision of the Study were in the hands of Louise Doswald-Beck and Jean-Marie Henckaerts. ‘The authors, jointly, bear the sole responsibility for the content of the study’ (p. xlix). ‘[The] ICRC respected the academic freedom both of the report's authors and of the experts consulted’ (p. xi).

26. The large collection of found practice was made available for two purposes: the reader is thus permitted to verify the basis that was used to establish each rule and it provides practitioners and scholars with an immense collection of information that might be useful for their own professional objectives (p. xlviii).

27. The collection of materials and the consultation process was concluded on 31 December 2002, so that events taking place after that could not be taken into consideration. Some topics that seemed fairly evident, such as granting prisoner-of-war status, appeared not to be so after, for example, the Guantánamo Bay situation. It was argued that a great number of individuals held in Guantánamo Bay could not be regarded as civilians, nor did their situation meet the legal requirements attached to prisoner-of-war status. They were consequently deprived of rights attached to either status. This position regarding their status is considered to be highly controversial.

28. Although exceeding the scope of this review, a worthwhile theoretical and methodological examination could be conducted into other legal theories that might have been suitable to serve as a basis but were not selected as such.

29. Conclusion in A. M. Slaughter and S. R. Ratner, ‘Appraising the Methods of International Law: A Prospectus for Readers’, (1999) 93 (2) AJIL 291, at 292.

30. The symposium's queries are addressed to a selection of seven major methods representative of international legal scholarship: legal positivism, the New Haven School, international legal process, critical legal studies, international law and international relations, feminist jurisprudence, and law and economics, ibid., at 293.

31. With the arguable exception of critical legal studies (CLS), which does not propose to establish a method different from or contradictory to the various existing approaches. Rather CLS represents a manner of viewing international law choosing to emphasize the general failures of the international legal process and to provide critical constructive criticism to that process.

32. A. M. Slaughter and S. R. Ratner, ‘The Method is the Message’, (1999) 93 (2) AJIL 410, at 412.

33. Slaughter and Ratner, supra note 29, at 293. See also H. McCoubrey and N. D. White, Textbook on Jurisprudence (1996); H. Kelsen, Principles of International Law (1952), 438–9.

34. North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands), Judgment, 20 February 1969, [1969] ICJ Rep. 4, at 3, para. 77.

35. S. W. Jevons, Elementary Lessons in Logic, Deductive and Inductive: ‘with copious questions and examples and a vocabulary of logical terms’ (1918) (emphasis in original).

36. A. E. Roberts, ‘Traditional and Modern Approaches to Customary International Law: A Reconciliation’, (2001) 95 (4) AJIL 757, at 758.

37. O. Corten, ‘The Controversies over the Customary Prohibition on the Use of Force: A Methodological Debate’, (2005) 16 EJIL 803.

38. Ibid., at 804.

39. T. Meron, The Humanization of International Law (2006), 361.

40. See Corten in discussing the extensive approach, supra note 37, at 803.

41. Corten identifies this as the restrictive approach, ibid.

42. Formal sources provide legal procedures and methods for the creation of rules of general application. These rules have a legally binding effect. In turn, material sources provide evidence that proves the existence of rules of general application that have legally binding effect. However, in international law it is difficult to maintain a clear distinction between formal and material sources. For further general discussion see I. Brownlie, Principles of Public International Law (2003), 3; O. Schachter, in R. MacDonald and D. M. Johnston (eds.), The Structure and Process of International Law (1983), 745; V. D. Degan, Sources of International Law (1997).

43. M. Byers, ‘The Shifting Foundations of International Law: A Decade of Forceful Measures against Iraq’, (2002) 13 EJIL 21, at 25. On this analysis see Corten, supra note 37, at 812.

44. The current paper does not reflect doctrinal debate that pleads to make a distinction between general customary law and special or regional customary law.

45. As argued by M. Sassòli during the ICRC Conference on the occasion of the publication of the Study, October 2005, in Montreal, ‘The study strictly applies theory of customary law but proves that the “old” theory doesn't work.’ This view is promulgated by Sir Robert Jennings, Reflections on the Subsidiary Means for the Determination of Rules of Law (2003); R. Y. Jennings, ‘The Judiciary, International and National, and the Development of International Law’, (1996) 45 ICLQ, at 1.

46. Sassòli, supra note 45. The argument is that non-state actors, such as armed groups, contribute to creating custom because custom is formed by the addressees of the rule. The ICRC is very cautious towards this approach, saying that its legal significance is unclear, and has listed such practice under ‘other practice’ that might be evidence of acceptance of rules. Comparably, under the law of the sea every captain can contribute to the formation of the rules; under international humanitarian law could any soldier do the same? Certainly not when that individual soldier is condemned and/or punished for his or her behaviour, but what if the soldier's actions are condoned by one or more superiors? Would that make the situation different?

47. The Court addresses this in several cases, particularly in the North Sea Continental Shelf cases, supra note 34.

48. Ratner and Slaughter, supra note 32, at 411.

49. Prosecutor v. Tadić, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, Case No. IT-94–1-T, T.Ch. II, 2 October 1995, para. 99. The opposite is also held. ‘[I]t focuses on statements to the exclusion of acts and relies on a government's words rather than deeds. Yet, war is the ultimate test of law. Government-authorized actions in war speak louder than peacetime government statements.’ H. Parks, ‘The ICRC Customary Law Study: A Preliminary Assessment’, Proceedings of the Annual Meeting – American Society of International Law, 99 (2005), 208, at 210. Parks's initial suggestion that the ICRC Study lacks battlefield practice is primarily based on his observations in relation to the ICRC rules on weapons.

50. Military circles are generally dissatisfied with the inclusion of military manuals as state practice, and maintain that primary reliance should be placed on battlefield practice instead. It is important to note that battlefield practice was not excluded from the study but included to the extent possible, meaning to the extent that it could be identified, since battlefield practice is extremely difficult to assess due to the characteristics of armed conflict situations (p. xxxii). For more detailed remarks see Garraway's argument that military manuals are policy documents: C. Garraway, ‘The Use and Abuse of Military Manuals’, (2004) 7 Yearbook of International Humanitarian Law 425. Similarly, Greenwood identifies the German manual reference to Common Article 3 as being a policy application of Germany rather than a statement about the existing state of the law: C. Greenwood, ‘International Humanitarian Law and the Tadić Case’, (1996) 7 EJIL 265, at 276.

51. Some claim that military manuals are at a minimum opinio juris, since they contain instruction to troops on how to behave during armed conflicts. The question of how this practice/opinio juris contributes to the formation of customary law is another matter. The answer is found in the reactions to the practice; how is it received by other states? Is it considered to be in accordance with the law or is it considered a breach, as deviant behaviour? It is important to emphasize this because otherwise the ongoing practice of torture, for example, would develop to be the rule. It is the actual condemnation of such practice that reaffirms the prohibition of torture.

52. An example would be British case law condemning military personnel for the assault and ill-treatment of detainees in Iraq. However, national jurisprudence involving such cases is not widely available.

53. The Study does not explain further why the jurisprudence of international courts is considered ‘persuasive evidence’.

54. J. Klabbers, ‘International Organizations in the Formation of Customary International Law’, in E. Cannizzaro and P. Palchetti (eds.), Customary International Law on the Use of Force (2005), 179 at 195.

55. Ibid., at 180.

56. U. Fastenrath, ‘Relative Normativity in International Law’, (1993) 4 EJIL 317.

57. See also Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 8 July 1996, [1996] ICJ Rep. 66, at 254–5, paras. 70–73.

58. Asylum case (Columbia v. Peru), Judgment, 20 November 1950, [1950] ICJ Rep. 266; Fisheries case (United Kingdom v. Norway), Judgment, 18 December 1951, [1951] ICJ Rep. 116, at 138.

59. Fisheries Case, supra note 58, at 138.

60. Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States), Judgment, 27 June 1986, [1986] ICJ Rep. 14, at 98, para. 186.

61. Ibid.; see also the Study, p. xxxviii. Many frequent violations of international humanitarian law are accompanied by a vast amount of verbal state practice comprising evidence supporting the breached rule(s).

62. The jurisprudence of the ICJ, in particular in the Nicaragua case, begs the question how often a violation of a norm is required in order to be able to conclude that the norm ceases to exist.

63. North Sea Continental Shelf cases, supra note 34, at 43, para. 74.

64. ILA Final Report of the Committee on the Formation of Customary (General) International Law, statement of principles applicable to the formation of general customary international law, Report of the Sixty-Ninth Conference, London, 2000, Principle 14, Commentary (d) and (e), at 736–7.

65. The text of Rule 144 reads as follows: ‘States may not encourage violations of international humanitarian law by parties to an armed conflict. They must exert their influence, to the degree possible, to stop violations of international humanitarian law.’ Supporting practice can be found in Vol. II, Chapter 41, Section A. The ICRC does indicate that some specific areas of international humanitarian law do ‘specially affect’ certain states, depending on the issue and the circumstances.

66. This seems a wide-ranging statement that does not provide answers to the questions it triggers, for example, whether the practice of specially affected states is accorded more weight than the practice of states not specially affected. It is also quite contrary to what was done in the San Remo Manual, in which only the practice of specially affected states, meaning seafaring states, was taken into account. L. Doswald-Beck (ed.), San Remo Manual on International Law Applicable to Armed Conflicts at Sea (1995).

67. For more information on this issue see L. Condorelli, ‘Nuclear Weapons: A Weighty Matter for the International Court of Justice’, (1997) 316 International Review of the Red Cross 9; J. Currie, Public International Law (2001), 176; H. Thirlway, ‘The Sources of International Law’, in M. Evans (ed.), International Law (2003), at 117; M. Villiger, Customary International Law and Treaties (1997), at 35; ILA Final Report, supra note 64, commentary (b) to principle 15.

68. Conference transcripts, statement J.-M. Henckaerts (on file with author).

69. See for instance the Report by the Special Representative of the Commission of Human Rights on the Situation of Human Rights in El Salvador, UN Doc. A/38/53, 22 November 1983.

70. See further J. F. Quéguiner, ‘Direct Participation in Hostilities under International Humanitarian Law’, Working Paper, 2003, International Humanitarian Law research initiative ‘Reaffirmation and Development of IHL: Direct Participation in Hostilities under International Humanitarian Law’, Program on humanitarian policy and conflict research at Harvard University (the ‘Alabama Process’); see http://www.ihlresearch.org/portal/ihli/alabama.php.

71. Prosecutor v. Tadić, Opinion and Judgement, Case No. IT-94–1, T. Ch. II, 7 May 1997, at para. 616.

72. The first two expert meetings were convened on 27–9 January 2003 and 25–27 June 2004 respectively. The Third Informal High-Level Expert Meeting on Current Challenges to International Humanitarian Law took place in Montreux, Switzerland, on 22–4 May 2006.

73. Henckaerts, for example, issued a firm rebuttal in his ‘Customary International Humanitarian Law: A Response to US Comments’, (2007) 89 International Review of the Red Cross 473.

74. R. A. Kok, Statutory Limitations in International Criminal Law (2007). Kok refers to Vol. I, pp. 614–18, and Vol. II, pp. 4044–73, of the ICRC Study.

75. Statement by Lt. Col. B. Carnahan, Launching the conference on the ICRC Study, ‘The Reaffirmation of Custom as an Important Source of International Humanitarian Law’, Washington College of Law, 28 September 2005.

76. Particular concern is raised with respect to individuals who are subject to interrogation while in captivity. What type of interrogation techniques are or are not considered acceptable under ‘humane treatment’?

77. Statements at launching conferences of the Study, e.g. ‘The Reaffirmation of Custom as an Important Source of International Humanitarian Law’, supra note 75; Canadian Red Cross and McGill University, ‘Customary International Humanitarian Law: Challenges, Practices and Debates’, Montreal, 29 September–1 October 2005.

78. Additional Protocol I, 1977, Art. 56, Protection of Works and Installations Containing Dangerous Forces.

79. As is the case in assessing the weight of a particular resolution, the weight of a particular treaty is assessed by looking at ‘reservations and statements of interpretation made upon ratification’ (p. xliii), but also at the widely ratified or universal status of treaties such as the UN Charter (p. xliii).

80. It is said that practice contributing to a rule of customary international law should per se be practice of states not party to a treaty since the practice of states parties does not reflect custom but is practice under treaty obligations. It is true that the first type of practice is a good indicator of (emerging) customary rules, but it could not be the only form of practice that should be taken in account, since custom would then be a rule created by a minority of states that is binding on all states. ‘A rule of customary international law is only emerging when there is acquiescence and positive practice.’ Statement by L. Doswald-Beck, September 2005 (on file with author).

81. The introduction of exploding anti-aircraft bullets in the First World War did not trigger any protest (pp. 272–3).

82. The text of Rule 78 reads as follows: ‘The anti-personnel use of bullets which explode within the human body is prohibited.’

83. 1997 Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-personnel Mines and on Their Destruction.

84. Non-signatory states to the convention, such as China, Finland, India, South Korea, Pakistan, Russia, and the United States, consider that they are allowed to use anti-personnel mines (p. 282).

85. The text of Rule 81 reads as follows: ‘When landmines are used, particular care must be taken to minimize their indiscriminate effects’ (p. 280).

86. These are Rule 82, ‘A party to the conflict using landmines must record their placement, as far as possible’, and Rule 83, ‘At the end of active hostilities, a party to the conflict which has used landmines must remove or otherwise render them harmless to civilians, or facilitate their removal’ (pp. 283, 285).

87. The text of Rule 86 reads as follows: ‘The use of laser weapons that are specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision is prohibited’ (p. 292).

88. See also North Sea Continental Shelf cases, supra note 34, at 44, para. 74.

89. When launching conferences or in individual articles (Henckaerts).

90. Prosecutor v. Tadić, supra note 49.

91. ‘Like the Nuremberg and Tokyo trials, the trial of the first defendant in the custody of the new ad hoc war crimes tribunal for the former Yugoslavia is foundational in that it seeks not only to effect legal justice for Tadić but to reinvigorate the Nuremberg principles, and indirectly, the rule of law. It is political insofar as intended to deter future war crimes, make reconciliation possible in the former Yugoslavia, and help restore peace.’ J. E. Alvarez, ‘Numbering Revisited: The Tadić Case’, (1996) 7 EJIL 245, at 245.

92. For a thorough analysis see C. Greenwood, supra note 50, at 275–6, discussing aspects of the development of customary international humanitarian law. See also D. Turns, ‘At the “Vanishing Point” of International Humanitarian Law: Methods and Means of Warfare in Non-international Armed Conflicts’, 2002 German Yearbook of International Law 45, at 115.

93. See Alvarez, supra note 91, at 277: ‘[I]t discussed at length the evolution of customary international law rules relating to the conduct of hostilities . . . in internal conflicts, notwithstanding that this body of substantive law was not relevant to the Tadić case’.

94. Turns, supra note 92, at 130.

95. R. Y. Jennings, ‘What Is International Law and How Do We Tell When We See It?’, (1981) 37 Schweizerisches Jahrbuch für internationales Recht 59, at 67.