¹ See, e.g., F. Ost and M. van de Kerchove, De la pyramide au réseau? Pour une théorie dialectique du droit (2002); Peters, A., ‘Fragmentation and Constitutionalization’, in Orford, A. and Hoffmann, F. (eds.), The Oxford Handbook of the Theory of International Law (2016) 1011 Google Scholar; I. Raducu and N. Levrat, ‘Le métissage des ordres juridiques européens’, (2007) Cahiers de droit européen 111; M.A. Young, Regime Interaction in International Law – Facing Fragmentation (2012).

² On the development of this concept see Itzcovich, G., ‘Legal Order, Legal Pluralism, Fundamental Principles. Europe and Its Law in Three Concepts’, (2012) ELJ 358 Google Scholar.

³ For the classification of legal orders as autopoietic systems see N. Luhmann, Das Recht der Gesellschaft (1993), 38 et seq.; for further discussion see M. van de Kerchove and F. Ost, Le système juridique entre ordre et désordre (1988), 150 et seq.; A. Peters, Elemente einer Theorie der Verfassung Europas (2001), 509 et seq.

⁴ For an approach that involves the concept of hybridity in relation to the state/non-state relationship see Berman, P. Schiff, ‘Towards a Jurisprudence of Hybridity’, (2010) 1 Utah Law Review 11 Google Scholar.

⁵ Schilling, T., ‘The Autonomy of the Community Legal Order: An Analysis of Possible Foundations’, (1996) 37 Harvard International Law Journal 389 Google Scholar; Peters, A., ‘Rechtsordnungen und Konstitutionalisierung: Zur Neubestimmung der Verhältnisse’, (2010) Zeitschrift für öffentliches Recht 3, at 31Google Scholar et seq.

⁶ For the other dimensions of autonomy see Peters, supra note 5, at 31 et seq.

⁷ See, e.g., E. Melissaris, Ubiquitous Law: Legal Theory and the Space for Legal Pluralism (2009), in particular Chapter 2. Further regarding legal pluralism see Berman, P. Schiff, ‘Global Legal Pluralism’, (2007) 80 Southern California Law Review 1155 Google Scholar; Burke-White, W., ‘International Legal Pluralism’, (2004) 25 Michigan Journal of International Law 963 Google Scholar; Klabbers, J. and Piiparinen, T. (eds.), Normative Pluralism and International Law: Exploring Global Governance (2013)CrossRefGoogle Scholar; Fischer-Lescano, A. and Teubner, G., ‘Regime Collisions: The Vain Search for Legal Unity in the Fragmentation of International Law’, (2004) 25 Michigan Journal of International Law 999 Google Scholar; Zumbansen, P., ‘Transnational Legal Pluralism’, (2010) 1 Transnational Legal Theory 141 CrossRefGoogle Scholar.

⁸ For an additional explicit focus on heterarchy see, e.g., Halberstam, D., ‘Constitutional Heterarchy: The Centrality of Conflict in the European Union and the United States’, in: Dunoff, J. and Trachtman, J. (eds.), Ruling the World? Constitutionalism, International Law and Global Governance (2009), 326 CrossRefGoogle Scholar.

⁹ Terminology used by De Witte, B., ‘Retour à «Costa», La primauté du droit communautaire à la lumière du droit international’, (1983) RTDE 425, at 427Google Scholar.

¹⁰ Ibid.

¹¹ See, e.g., Shelton, D. (ed.), International Law and Domestic Legal Systems: Incorporation, Transformation and Persuasion (2011)CrossRefGoogle Scholar.

¹² See, e.g., with regard to the peremptory character of the European Convention on Human Rights according to the jurisprudence of the European Court of Human Rights (ECtHR), Gardbaum, S., ‘Human Rights as International Constitutional Rights’, (2008) 19 EJIL 749 CrossRefGoogle Scholar, at 756 et seq.

¹³ See, e.g., R. Barents, The Autonomy of Community Law (2004).

¹⁴ Besson, S., ‘How international is the European legal order?’, (2008) No Foundations 50, at 60Google Scholar; also problematizing perspectivism: Tietje, C., ‘Autonomie und Bindung der Rechtsetzung in gestuften Rechtsordnungen’, (2007) 66 Veroffentlichungen der Vereinigung der Deutschen Staatsrechtslehrer 45 Google Scholar, at 51.

¹⁵ Kumm, M., ‘The Cosmopolitan Turn in Constitutionalism: On the Relationship between Constitutionalism in and beyond the State’, in Dunoff, J. and Trachtman, J. (eds.), Ruling the World? Constitutionalism, International Law and Global Governance (2009), 258 CrossRefGoogle Scholar at 310.

¹⁶ Duguit, L., Traité de droit constitutionnel (1927), vol. I, at 96Google Scholar; H. Kelsen, Das Problem der Souveränität und die Theorie des Völkerrechts (1928), 111; Scelle, G., Précis de droit des gens (1932), vol. I, at 39Google Scholar; Verdross, A., Die Verfassung der Völkerrechtsgemeinschaft (1926), 17, 29 et seqGoogle Scholar.

¹⁷ D. Anzilotti, Lehrbuch des Völkerrechts (1929), 42; H. Triepel, Völkerrecht und Landesrecht (1899), 30, 32.

¹⁸ For a discussion of these concepts as well as of their interrelation see Peters, supra note 1, at 1011.

¹⁹ See, e.g., Michaels, R. and Pauwelyn, J., ‘Conflict of Norms or Conflict of Laws?: Different Techniques in the Fragmentation of Public International Law’, (2012) 22 Duke Journal of Comparative & International Law 349 Google Scholar.

²⁰ See, e.g., N. MacCormick, ‘Beyond the Sovereign State’, (1993) Modern Law Review 1; Richmond, C., ‘Preserving the Identity Crisis: Autonomy, System and Sovereignty in European Law’, (1997) 16 Law and Philosophy 377 Google Scholar.

²¹ For a critique see, e.g., N. Walker, ‘The Idea of Constitutional Pluralism’, (2002) Modern Law Review 317; Kumm, M., ‘The Cosmopolitan Turn in Constitutionalism: On the Relationship between Constitutionalism in and beyond the State’, in Dunoff, J. and Trachtman, J. (eds.), Ruling the World? Constitutionalism, International Law and Global Governance (2009), 258 CrossRefGoogle Scholar at 311 et seq.

²² Thus, the theoretical dimension of the concept of autonomy can be gradual as well. See regarding the different dimensions of autonomy Peters, supra note 5, at 31.

²³ It may be stressed that it is the actual legal norm and not ‘merely’ the legal space which is characterized by hybridity. For an approach of a ‘hybridity of legal spaces’ see Berman, P. Schiff, ‘Global Legal Pluralism’, (2007) 80 Southern California Law Review 1155 Google Scholar.

²⁴ Also, this analysis spells out the extent to which the process of implementation qualitatively goes further than a pure mechanism of transformation of international law into domestic norms as required by a dualist approach to the relationship between the domestic and the international legal order.

²⁵ For the broad application of the concept of positive obligations by the Inter-American Court of Human Rights see, e.g., L. Lavrysen, ‘Positive Obligations in the Jurisprudence of the Inter-American Court of Human Rights’, [2014] Inter-American and European Human Rights Journal 94; Regarding the use by the ECtHR see A. Mowbray, The Development of Positive Obligations under the European Convention on Human Rights by the European Court of Human Rights (2004).

²⁶ Regarding the Inter-American human rights framework, the obligation to take legislative measures of implementation is explicitly enshrined in Art. 2 of the American Convention on Human Rights. See also Inter-American Court of Human Rights, ‘The Last Temptation of Christ’ (Olmedo-Bustos et al.) v. Chile, Judgment of 5 February 2001, Series C, No. 73, para. 87: ‘In international law, customary law establishes that a State which has ratified a human rights treaty must introduce the necessary modifications to its domestic law to ensure the proper compliance with the obligations it has assumed. This law is universally accepted, and is supported by jurisprudence. The American Convention establishes the general obligation of each State Party to adapt its domestic law to the provisions of this Convention, in order to guarantee the rights that it embodies.’

²⁷ See Art. 70 concerning offences against the administration of justice.

²⁸ See in particular Art. 4 of the 1984 Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, 1465 UNTS 85.

²⁹ See in particular Art. VII, para. 1 of the 1993 Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction, 1974 UNTS 45.

³⁰ See in particular Art. 3 and Art. 8 para. 2 of the OECD 1997 Convention on Combating Bribery of Foreign Public Officials in International Business Transactions.

³¹ See in particular Arts. 4–6 of the 1999 UN Convention for the Suppression of the Financing of Terrorism, 2178 UNTS 197.

³² See in particular Arts. 15–42 of the 2003 UN Convention Against Corruption, 2349 UNTS 41 (although some of these provisions do not create immediate obligations of implementation).

³³ For an approach that attributes a central role to general principles in the articulation of legal orders, regimes and norms in the international context see Jouannet, E. Tourme, ‘L'ambivalence des principes généraux face au caractère étrange et complexe de l'ordre juridique international’, in Vinaixa, R. Huesa and Wellens, K. (eds.), L'influence des sources sur l'unité et la fragmentation du droit international (2006), 115 Google Scholar at 134 et seq.

³⁴ The terms ‘horizontal’ and ‘vertical’ are used for the sake of clarity, not as a statement in favour of a hierarchical relationship between international and domestic law.

³⁵ For this comparative approach see Case Concerning Oil Platforms (Islamic Republic of Iran v. United States of America), Judgment of 6 November 2003, [2003] ICJ Rep. 161, and 324 (Judge Simma, Separate Opinion) at para. 66.

³⁶ For an overview regarding this mechanism see A. Nollkaemper, National Courts and the International Rule of Law (2011), 139 et seq; Betlem, G. and Nollkaemper, A., ‘Giving effect to public international law and European Community law before domestic courts – A comparative analysis of the practice of consistent interpretation’, (2003) 14 EJIL 569 CrossRefGoogle Scholar; see also Betlem, G., ‘The doctrine of consistent interpretation – managing legal uncertainty’, (2002) 22 Oxford Journal of Legal Studies 397 CrossRefGoogle Scholar.

³⁷ In the EU law context, the concept of consistent interpretation is not only directed from the domestic legal orders towards supranational law but also reciprocally from the supranational legal order towards domestic – constitutional – law. See A. Peters, Elemente einer Theorie der Verfassung Europas (2001), 289 et seq.

³⁸ For a comparable observation concerning the EU law context see Raducu and Levrat, supra note 1, at 118.

³⁹ For an approach that considers cross-regime interpretation as a systemic element in the international legal sphere see Matz-Lück, N., ‘Norm Interpretation across International Regimes: Competences and Legitimacy’, in Young, M.A. (ed.), Regime Interaction in International Law – Facing Fragmentation (2012), 201 Google Scholar at 211 et seq.

⁴⁰ Stichting Mothers of Srebrenica and Others v. the Netherlands (dec.), no. 65542/12, § 139, ECHR 2013.

⁴¹ Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory (Request for advisory opinion), Advisory Opinion of 9 July 2004, [2004] ICJ Rep. 136, para. 104 et seq; The Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion of 8 July 1996, [1996] ICJ Rep. 226, para. 25.

⁴² For an analysis of this provision see McLachlan, C., ‘The Principle of Systemic Integration and Article 31(3)(c) of the Vienna Convention’, (2005) 54 International and Comparative Law Quarterly 279 CrossRefGoogle Scholar.

⁴³ See, e.g., the German Federal Constitutional Court, Order of 1 March 2004, 2 BvR 1570/03, para. 12: ‘The Basic Law is intended to accommodate international law. . .and hence as a rule may not be interpreted in such a way to give rise to a conflict with obligations of the Federal Republic of Germany under international law.’ Regarding this German constitutional law concept see also Payandeh, M., ‘Völkerrechtsfreundlichkeit als Verfassungsprinzip’, (2009) 57 Jahrbuch des öffentlichen Rechts der Gegenwart 465 Google Scholar. For a similar approach of the Czech Constitutional Court regarding the obligation of consistent interpretation in the EU legal context see the Dec. Pl. ÚS 66/04 of 3 May 2006, para. 61: ‘A constitutional principle can be derived from Article 1 par. 2 of the Constitution, in conjunction with the principle of cooperation laid down in Art. 10 of the EC Treaty, according to which domestic legal enactments, including the constitution, should be interpreted in conformity with the principles of European integration and the cooperation between Community and Member State organs.’

⁴⁴ See, e.g., Casolari, F., ‘Giving indirect effect to international law within the EU legal order: the doctrine of consistent interpretation’, in Cannizzaro, E. et al. (eds.), International law as law of the European Union (2012), 269 Google Scholar.

⁴⁵ For an analysis of the extensive references of the International Criminal Tribunal for the former Yugoslavia to the jurisprudence of the ECtHR see Cassese, A., ‘The Impact of the European Convention on Human Rights on the International Criminal Tribunal for the Former Yugoslavia’, in Mahoney, P. et al. (eds.), Protection des droits de l'homme: la perspective européenne – Protecting Human Rights: The European Perspective, Mélanges à la memoire de/Studies in Memory of Rolv Ryssdal (2000), 213 Google Scholar.

⁴⁶ See references supra note 36. See also Kirby, M.D., ‘Transnational judicial dialogue, internationalisation of law and Australian judges’, (2008) 9 Melbourne Journal of International Law 171 Google Scholar.

⁴⁷ For some examples of the discussion see Slaughter, A.M., ‘A Global Community of Courts’, (2003) 44 Harvard International Law Review 191 Google Scholar; M.A. Waters, ‘The future of transnational judicial dialogue’, American Society of International Law: Proceedings of the 104th annual meeting (2011), 465; Harbo, T., ‘Legal integration through judicial dialogue’, in Fauchald, O.K. and Nollkaemper, A. (eds.), The practice of international and national courts and the (de-)fragmentation of international law (2012), 167 Google Scholar.

⁴⁸ For an early discussion of this phenomenon see McCrudden, C., ‘A Common Law of Human Rights?: Transnational Judicial Conversations on Constitutional Rights’, (2000) 20 Oxford Journal of Legal Studies 499 CrossRefGoogle Scholar.

⁴⁹ See Walker, N., ‘Sovereignty and Differentiated Integration in the European Union’, (1998) ELJ 355, at 375CrossRefGoogle Scholar; for a comparable approach regarding the ‘métissage’ of legal orders see Raducu and Levrat, supra note 1.

⁵⁰ For regime-related examples see the work of international organizations charged to harmonize international commercial and trade law standards that recommend adoption of model laws, which often reflect best practice in domestic jurisdictions. See, e.g., the work of the United Nations Commission on International Trade Law (UNCITRAL) and the International Institute for the Unification of Private Law (UNIDROIT).

⁵¹ See, e.g., Gardbaum, S., ‘Human Rights and International Constitutionalism’, in Dunoff, J. and Trachtman, J. (eds.), Ruling the world? Constitutionalism, International Law, and Global Governance (2009)Google Scholar.

⁵² Halmai, G., ‘The Use of Foreign Law in Constitutional Interpretation’, in Rosenfeld, M. and Sajó, A. (eds.), The Oxford Handbook of Comparative Constitutional Law (2012), 1328 Google Scholar.

⁵³ See regarding common procedural principles Kingsbury, B. and Casini, L., ‘Global Administrative Law: Dimensions of International Organizations Law’, (2009) 6 International Organizations Law Review 319 CrossRefGoogle Scholar, at 333.

⁵⁴ See, e.g., Harlow, C., ‘Global Administrative Law: The Quest for Principles and Values’, (2006) 17 EJIL 190 CrossRefGoogle Scholar.

⁵⁵ Judgment No. 2991, Administrative Tribunal of the International Labour Organization, Judgment of 2 February 2011, para. 13; see also De Merode et al. v. The World Bank, Decision No. 1 of June 5 1981, The World Bank Administrative Tribunal, para. 28.

⁵⁶ On the merely limited trumping impact of jus cogens norms on other international law norms see Vidmar, J., ‘Norm Conflicts and Hierarchy in International Law: Towards a Vertical International Legal System?’, in Wet, E. De and Vidmar, J. (eds.), Hierarchy in International Law: The Place of Human Rights (2012), 13 CrossRefGoogle Scholar; Wet, E. De and Vidmar, J., ‘Conclusions’, in Wet, E. De and Vidmar, J. (eds.), Hierarchy in International Law: The Place of Human Rights (2012) 300 CrossRefGoogle Scholar, at 307.

⁵⁷ Kelsen, H., ‘Der Begriff der Rechtsordnung‘, in Klecatsky, H., Marcić, R. and Schambeck, H. (eds.), Die Wiener Rechtstheoretische Schule (1968)Google Scholar, vol. 2, 1395 at 1400.

⁵⁸ See T. Schilling, Rang und Geltung von Normen in gestuften Rechtsordnungen (1994), 159 et seq.

⁵⁹ J. Raz, Concept of A Legal System (1970), 190.

⁶⁰ H.L.A. Hart, The Concept of Law (1965), 92, 97 et seq.

⁶¹ These criteria are addressed by the ‘identity problem’ according to Raz's understanding of legal systems, see Raz, supra note 59, at 1.

⁶² Certains intérêts allemands en Haute-Silésie polonaise – Fond, PCIJ, 25 May 1926, Series A, No. 7, at 19.

⁶³ See D. Burchardt, Die Rangfrage im europäischen Normenverbund (2015), 199 et seq.

⁶⁴ Unless assuming – what this article does not – a monist legal world on the one hand or a considerable quantity of explicit norms of transposition on the other which would ensure the legal existence of certain external norms within a legal order or regime.

⁶⁵ Other than the concept of monism, the approach suggested in this article is not based on a fully integrated, normatively homogenous legal sphere. The graduated character of the approach may be stressed here again.

⁶⁶ See supra at Section 2.

⁶⁷ Case C-115/09, Bund für Umwelt- und Naturschutz v. Arnsberg (Trianel), [2011] ECR I-3673.

⁶⁸ For such approaches see Besson, S., ‘How international is the European legal order?’, (2008) No Foundations 50, at 65Google Scholar; Kumm, M., ‘Rethinking Constitutional Authority: On the Structure and Limits of Constitutional Pluralism’, in Avbelj, M. and Komárek, J. (eds.), Constitutional Pluralism in the European Union and Beyond (2012), 39 at 55Google Scholar et seq.