International Law and Domestic Law

Author: Raffaela Kunz

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Learning objectives: Understanding XY.

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A. IntroductionEdit

The relationship between international and domestic law (or the synonyms national or municipal law) is an evergreen topic featuring in every textbook on public international law. What is the background? Since International law in the majority view is considered to be an autonomous legal system independent of domestic legal systems, the question arises how the two systems relate to and interact with one another. Even though the relationship between international and domestic law is thus a classic question, having been discussed and theorized extensively, it has not lost any of its currency. In recent years, with some high-profile cases of domestic courts contradicting or "resisting" International law and international courts (see in more detail below C.II.), the question has even gained renewed significance.

There is no simple answer to the question how international law and domestic law relate to one another. The starting point is that while international law asserts its primacy over domestic law and requires to be followed and implemented, it is usually left to the states to decide about the concrete modalities to do so. Sometimes the term "obligations of result" is used to describe this circumstance. In other words, international obligations stop "short at the outer boundaries of the State machinery". [2] In this sense, international law may „(...) insert its demands in the box, requiring certain results to come out of it; however, it cannot determine how these results are reached within the box.“[3] States thus retain a certain degree of freedom in the choice of means to implement their international obligations in the domestic legal sphere. This "freedom of implementation" is limited by the fact that states cannot invoke their domestic law to justify the non-fulfillment of their obligations. Article 3 of the Articles on the Responsibility of States for Internationally Wrongful Acts makes clear that the "characterization of an acts internationally wrongful "is not affected by the characterization of the same act as lawful by internal law." Article 27 of the Vienna Convention of the Law of Treaties furthermore states that a state "may not invoke the provisions of its internal law as justification for its failure to perform a treaty." The non-achievement of the required result thus leads to the responsibility of the state on the international plane (see also chapter on state responsibility).

What makes the situation even more complex is that in the decentralized international legal order, to large extents lacking centralized enforcement mechanisms, it is up to domestic actors to implement and enforce international law, with a primordial role in this regard played by domestic courts. Over the last decades, with international regulation more and more overlapping with subjects also regulated under domestic law, from human rights to the environment and health, conflicts between the two bodies of law have become more frequent.

B. Conceptualizing the RelationshipEdit

I. The Classic Theories and Their LimitsEdit

1. Preliminary RemarksEdit

There are two theories that give different answers as to how international and domestic law relate to each other: monism and dualism. Following the above-described freedom in the means to implement international law, it is up to states to decide whether they follow a monist or dualist model. One may argue that this prerogative of states supports the view that the legal reality rather corresponds to a dualist model. It is, however, important to clearly state from the outset that today neither of the two theories is ever fully realized in practice. Even dualist states often foresee exceptions for certain monist "exceptions"; and in monist states courts often reserve the right not to apply international law in certain cases (see in more detail below, C.II.).

The main question the theories seek to answer is how international law becomes valid within the domestic legal system, i.e. how it becomes law that is legally binding and relevant also within the domestic sphere. Monism and dualism foresee different answers to this question, the main difference being the level of involvement of parliament in the approval of international law. The question of validity is distinct from the question of the position of International law in the norm hierarchy or the question whether or not international law is directly applicable or self-executing by domestic courts and authorities (see on these questions below C.I). Given that in practice, these latter questions are more relevant than the formal validity of international law, the monism/dualism controversy already in the 50es has been criticized as "unreal, artificial and strictly beside the point".[4] Nonetheless, the theories continue to play a role in international legal practice and discourse. Today, a major point of discussion concerns the democratic legitimization of international law (see below II.).

2. DualismEdit

Dualism starts from the idea that international law and domestic law are two distinct legal orders and highlights the autonomy of both legal orders. As Heinrich Triepel, one of the main dualist theorists, has put it, international and domestic law are like "two circles that at most touch, but never intersect".[5] According to this dualist view, for an international legal norm to become valid in the domestic system, it needs to be "translated" to the domestic sphere trough an act of "transformation". Prominent states following a dualist model are Germany, the United Kingdom, India and Israel.

Among the dualist states, a further distinction is necessary. In the first group of states, including Germany, for International law to be transformed a formal parliamentary approval though a legislative act is sufficient. In Germany this act takes the form of a "Zustimmungsgesetz" in line with Art. 59(2) of the Basic Law. After the approval, the treaty can be applied as such, i.e. as International law. In the second group, a treaty can only be applied after having been implemented through substantive legislation. An example is the Human Rights Act[6] in the United Kingdom implementing the European Convention of Human Rights (currently again subject to reform discussions).[7] In this case, the law that will be applied domestically is not anymore the treaty, but the domestic implementing legislation.

3. MonismEdit

Contrary to dualism, monism considers international and domestic law to be one single legal order. According to Hans Kelsen, the most prominent theorist of monism, both international and domestic law derive their validity from one basic norm ("Grundnorm"). The main difference between monism and dualism in practice is that in the monist states, international law does not need to be transformed in order to acquire validity. In other words, international norms become automatically valid upon ratification. But Kelsen went even further, considering that any domestic rule contradicting international law is void. While Dualism can therefore be described with Triepel as two separate circles, monism according to Kelsen can be described with the form of a pyramid with International law on top.

Examples of monist states include the Netherlands, Switzerland, China and many Latin American Countries.

II. Current Debates: Is Dualism more Democratic than Monism?Edit

The main actor in the conclusion of treaties is the executive, a major difference to the domestic realm, where for democratic reasons parliament is the central law-making body. The involvement of parliament before a treaty becomes domestically binding law is thus to some extent a compromise to involve the democratically elected parliament before the law becomes binding domestically. However, many consider that in light of the important structural changes international law underwent, this is not enough anymore. While classic international law was very state-centered and regulated mainly inter-state issues, this has significantly changed, with today virtually no issue-area not touched upon by international regulation. This process has famously been described by Wolfgang Friedman as a transformation from a "law of coexistence" to a "law of cooperation".[8] This development has increased concerns about the democratic or "political deficit"[9] of big parts of the law governing today's societies.

Dualism, which entails a stronger involvement of parliament, is thus sometimes considered to be more democratic than monism. In light of the increased relevance of international law in some countries with a strong monist tradition, in recent years a shift to dualism has been discussed. By way of example, in Switzerland, a country with a strong direct democratic tradition, a (not successful) parliamentary motion in 2014 requested to consider a shift from monism to dualism. It argued that this would strengthen the Swiss legal order and its democratic legitimacy.[10] In the United Kingdom, in earlier discussions about the legal modalities of the UK's exit from the European Union, it was argued that dualism "may save the United Kingdom from Brexit".[11] The core of the argument was that exiting the Union would alter the UK's domestic law, making parliamentary involvement indispensable. Also some domestic courts in recent years have manifested a certain "dualist reflex" (see in more detail below C.II.).

However, dualism's democratic potential is overrated. Legislation transforming treaties of course needs to mirror the corresponding international obligations, in line with the basic principle that states are not allowed to invoke their domestic norms to deviate form international law (see above A.). The leeway parliament has is thus necessarily and inherently limited. And also in monist states such as Switzerland, the question wether parliament needs to be involved in the withdrawal from treaties, at least in the case of important treaties, is being discussed.[12] Neither dualims nor monisum thus seem to offer answers to the challenges and tensions arising in times of global governance and increased concerns for the legitimacy of the law. Some voices have thus argued that in the face of these challenges, especially domestic courts should be granted a certain flexibility when applying International law and facing unsolvable conflicts with domestic law. This will be addressed in more detail below (C.II and E.).

C. International Law in Domestic CourtsEdit

I. Questions Determining the Role of International LawEdit

Because of the decentralized nature of the international legal system, in practice it is often domestic actors and among those chiefly domestic courts that apply and implement international law. Until not so long ago, domestic courts were considered to be quite reluctant when it came to the application of international law. The reason was that the international arena was considered to be the exclusive realm of the executive branch.[13] This prompted the Institut de Droit International in 1993 to state that it was necessary "to strengthen the independence of national courts in relation to the Executive and to promote better knowledge of international law by such courts".[14] This situation has changed - due to the massive increase of international regulation leading to substantial overlaps with issues previously solely regulated under domestic law, domestic courts now regularly decide on cases involving international law. Today, domestic courts are considered to play an important role in filling gaps in the existing international legal order by applying international law. Since the international order lacks centralized law enforcement bodies, domestic courts play an important role in this regard and to some extent fill this gap. The idea is that by applying international law in domestic cases, courts "bring to life" international law and in this sense contribute to enforcing it.In line with George Scelle’s theory of dédoublement fonctionnel,[15] domestic judges thus not only fulfill a judicial function at the domestic level; they also have an international judicial function.[16] In light of this, it has been argued that courts contribute to strengthen the international rule of law.[17] In recent years, due to the increased activety of international courts and tribunal and the regulatory activities of international organisations, domestic courts not only deal with international treaties and custom, but increasingly also have to decide cases in which international judicial decisions or secondary rules play a role (see on this chapter XY). As will be discussed below (II.), recently cases make headlines in which domestic courts contradict their international counterparts or refuse to apply international law.

In the practice of domestic courts applying international law, the monism/dualism controversy hardly plays any role. More relevant are the questions whether international law in a given case is directly applicable or self-executing (synonym) and, in cases of a norm conflict, whether it prevails over conflicting domestic law. Put differently, the validity of international law is the necessary precondition for domestic actors to apply international law, but in practice the problems lie elsewhere. Another question that still plays some role is the political questions doctrine. These three issues shall be briefly discussed in the following.


2. Rank/hierarchyEdit

3. Political Questions DoctrineEdit

II. Recent Developments: "Backlash" Against International Law?Edit

Often, in the decentralized international legal system, great hope is being placed in domestic courts. Domestic judges are considered to play an important role in applying and enforcing international law in the absence of more centralized law enforcement mechanisms. While in the 90es it was still believed that domestic courts were reluctant to apply international law and even more so to take a stance that might contradict their domestic governments, it has been shown that over time, the application of international law by domestic courts has become quite normal (see above C.I.). Today, we might be witnessing yet another shift. Over the last years, there seems to be an increasing number of cases in which domestic courts explicitly refuse to apply international law and/or follow judgments of international courts. These cases have sometimes been called cases of "principled resistance".[18] To be sure, it is not a new phenomenon that domestic courts make clear that while they are open to international law and willing to contribute to its enforcement, there are certain limits. In Europe, many high courts have reserved the right to "defend" a certain constitutional core against the "intrusion" of European and international law, with the German Federal Constitutional Court being a well-known example.[19]

Yet, the number and diversity of these cases seems to be growing.[20] Today, they seem to span most jurisdictions and issue areas of international law. Much-discussed examples include the Italian Constitutional Court which in 2014 decided that the implementation of the judgment of the International Court of Justice in the jurisdictional immunities case (Germany v. Italy)[21] would violate the Italian constitution. It declared the law implementing the judgment to be unconstitutional, and, as a consequence, the ICJ judgment has not been implemented to this date.[22] In human rights law, examples include the Argentinian Supreme Court, which in 2017 refused to follow the Inter-American Court of Human Rights in the case of Fontevecchia and D'Amico,[23] and the Russian Constitutional Court, which even developed a certain "control of constitutionality" of judgments of the European Court of Human Rights (later translated into legislation).[24]

Interestingly, domestic courts often rely on constitutional values, including fundamental rights, when refusing to follow international law.[25] Rather than violating the rule of law, they thus seem to believe that they act in the interest of the rule of law. While these cases are often perceived as a setback or "backlash" against international law, this suggests that the reality is more complicated.[26] To be sure, in some cases the invocation of constitutional values and principles might be more of a pretext not to follow an undesired international norm. Overall, however, it is undeniable that with the massive growth of international regulation in quantitative terms and the proliferation of international courts, clashes between legal orders have simply become more likely.[27] Domestic courts can thus find themselves in a dilemma: on the one hand, they are "servants" to international law within the domestic realm and act as pivotal safeguards for its effectiveness. On the other hand, they remain "answerable to the dictates of applicable domestic law"[28] and, therefore, can be – and, in times of global governance and much increased activity of international courts, probably will be – increasingly torn between the sometimes conflicting commands of domestic and international law.[29] Of course there are no clear and simple answers to this dilemma. The question how these conflicts can be solve and how courts should accommodate to today's complex legal reality will be taken up again in the last section.

D. Domestic Law in International CourtsEdit

If domestic courts are regularly applying international law, what does the reverse case look like - how do international courts deal with domestic law? Here, the starting point is of course different. Even though domestic courts are not automatically bound by international law (whether they are depends on whether the state in question follows a monist/dualist system, whether the norm in question is directly applicable, etc.), it is clear that ultimately the obligations are binding on the state and need to be implemented (even though the concrete modalities are left to the states). In other words, domestic courts applying international law contribute to fulfill the international legal duties of their states. International courts, on the other hand, are not bound by domestic law and cannot said to contribute to fulfilling a broader duty. Against this background, it is not surprising that international courts have been reluctant when it comes to the application of domestic law. The Permanent Court of International Justice had expressed a very narrow view by stating that "[f]rom the standpoint of International Law and of the Court which is its organ, municipal laws are merely facts which express the will and constitute the activities of States".[30]

Today, it is, however, well recognized that domestic law also plays a role on the international plane. This is obvious when it comes to the formation of international law: domestic legislation plays a role in the formation of general principles of international law, and the decisions of domestic courts are seen as reflecting state practice, thus contributing to the formation of customary international law.[31] It has furthermore been argued that "(...) domestic law is sometimes a necessary component in the functioning of an international rule itself: the determination of nationality for the purposes of diplomatic protection or the definition of the rights of a shareholder are prime examples."[32]

But the relevance of domestic law on the international plane does not end there. It has been shown that the structural changes of international law, moving away from purely inter-state issues towards more and more issue areas previously only regulated by domestic law, has not only led to a more frequent application of international law by domestic actors, but more generally has had the consequence that "(...) the line between domestic and international law is increasingly blurred, with legal concepts, rules and principles crossing freely between the two spheres."[33] Today, just as international law plays a role when domestic courts apply and interpret the law, the same is true the other way around. While inter-state courts, such as the ICJ, are still cautious in relying on domestic law in their judgments, in other areas of law domestic law is an inherent part of the legal system, such as in the "margin of appreciation"/consensus doctrine of the European Court of Human Rights.[34] The European Court of Human Rights has furthermore made clear in its jurisprudence that the interpretation and development of the Convention standards is a joint endeavor, a "shared responsibility" between domestic courts and the European Court of Human Rights.[35] In some cases, it has even been criticized that the European Court of Human Rights in the face of political pressure coming from some state and political actors, has "given in" and overadjusted to domestic actors, risking its credibility.[36]

E. Conclusion: Accommodating Orders in a Complex Legal RealityEdit

The previous sections have shown that today, domestic and international law are not neatly separated legal orders, but rather strongly intertwined and mutually influential. With the body of international law growing quantitatively and expanding into more and more issue areas previously regulated solely by domestic law, it is clear that the legal reality has become more complex. It is thus not so surprising that clashes between norms have become more frequent. The question how the relationship between domestic law and international law should be theorized, and how concrete cases of conflict between the two bodies of law should be solved, in a way has become more timely than ever. Confronted with this complex legal reality, some domestic courts have started to develop criteria how to solve legal conflicts. A pattern we can observe over the last years is that a seemingly growing number of domestic courts has started to make explicit that the domestic constitution, or at least a certain core of the domestic constitution, in case of conflict with international law, would prevail (see above C.II.). While it seems to be too far-reaching to see these cases as cases of "backlash", undermining the relevance of international law, it might well be questionable whether in times of global governance and strong overlap between legal orders, such at first sight simple and clear conflict solutions are the right way to go. A more flexible approach, allowing to balance the different rights and interests at stake in a given case, even though less clear than strict conflict rules and hierarchies, might better fit today's complex legal reality.

Further ReadingsEdit

  • Source I
  • Source II


  • Summary I
  • Summary II

Table of ContentsEdit

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Part I - History, Theory, and Methods

Part II - General International Law

Part III - Specialized Fields


  1. The first footnote. Please adhere to OSCOLA when formating citations. Whenever possible, provide a link with the citation, ideally to an open-access source.
  2. ILC, Report of the Commission to the General Assembly on the Work of Its Twenty-Ninth Session, 9 May–29 July 1977, Commentary to the Draft Articles on State Responsibility, Breach of an international obligation requiring the achievement of a special result adopted on first reading, ILC YB 1977, Part Two, Art. 21 Abs. 1.
  3. Ward Ferdinandusse, Out of the Black Box? The International Obligation of State Organs, Brooklyn Journal of International Law 29 (2003), 45–127, 48.
  4. Gerald Fitzmaurice, The General Principles of International Law Considered from the Standpoint of the Rule of Law, Recueil des Cours 92 (1957), 71.
  5. Heinrich Triepel, Völkerrecht und Landesrecht, Leipzig 1899 (unveränderter Nachdruck Aalen 1958), S. 111.
  6. Human Rights Act of 9th November 1998, available at
  7. See on the government's reform proposal Colm O'Cinneide Having its (Strasbourg) Cake, and Eating It: The UK Government's Proposals for a New 'Bill of Rights', Völkerrechtsblog, 26.01.2022, doi: 10.17176/20220126-180053-0.
  8. Wolfgang Friedman, The Changing Structure of International Law (New York: Columbia University Press 1964). See also Joseph Weiler, The Geology of International Law, ZaöRV 64 (2004), 547; Bruno Simma, From Bilateralism to Community Interest International Law, RdC 250 (1994), 217.
  9. Isabelle Ley, Opposition in International Law – Alternativity and Revisibility as Elements of a Legitimacy Concept for Public International Law, Leiden Journal of International Law 28 (2015), 717, at 720.
  10. Parliamentary motion no. 14.3221, "Dualismus statt Monismus", Lukas Reimann, 21 March 2014, available at
  11. Julian Ku, How Dualism May Save the United Kingdom from Brexit, OpinioJuris, 3 November 2016,
  12. See e.g. Nina Blum, Vera Nägeli and Anne Peters, Die verafssungsmässigen Beteiligungsrechte der Bundesversammlung und des Stimmvolkes an der Kündigung völkerrechtlicher Verträge, ZBl 114 (2013), 527.
  13. On the traditional deference of domestic courts towards the executive on the international plane, see Eyal Benvenisti, ‘Reclaiming Democracy: The Strategic Uses of Foreign and International Law by National Courts’, American Journal of International Law 102 (2008), 241–274, at 241; Eyal Benvenisti/George W Downs, Between Fragementation and Democracy: The Role of National and International Courts (Cambridge: CUP 2017), at 105.
  14. Institut de droit international, ‘The Activities of National Judges and the International Relations of their State’, 7 September 1993, available at
  15. Georges Scelle, ‘Le phénomène juridique du dédoublement fonctionnel’, in Walter Schätzel/Hans-Jürgen Schlochauer (eds), Rechtsfragen der Internationalen Organisation. Festschrift für Hans Wehberg (Frankfurt am Main: Verlag Klostermann 1956), 324–342.
  16. Yuval Shany, ‘Dédoublement fonctionnel and the Mixed Loyalities of National and International Judges’, in Filippo Fontanelli/Giuseppe Martinico/Paolo Carrozza (eds), Shaping Rule of Law Trough Dialogue: International and Supranational Experiences (Groningen: Europa Law Publishing 2010), 29–42.
  17. André Nollkaemper, National Courts and the International Rule of Law (Oxford: OUP 2011).
  18. This term has been used in the context of the European Court of Human Rights. See Fiona de Londras/Kanstantsin Dzehtsiarou, ‘Mission Impossible? Addressing Non-Execution through Infringement Proceedings in the European Court of Human Rights’, International and Comparative Law Quarterly 66 (2017), 467–490. For a critical answer, see Alice Donald, ‘Tackling Non-Implementation in the Strasbourg System: The Art of the Possible?’, EJIL:Talk!, (28 April 2017), available at See also Marten Breuer, ‚Principled Resistance‘ to ECtHR Judgments: Dogmatic Framework and Conceptual Meaning, in Marten Breuer (Hrsg.), Principled Resistance to ECtHR Judgments – A New Paradigm? (Berlin/Heidelberg: Springer 2019), 3–34.
  19. Federal Constitutional Court (Germany) BvL 52/71, Solange I, 29 May 1974, BVerfGE 37, at 271; for more examples, see Peters, ‘The Globalization of State Constitutions’, in J.E. Nijman and A. Nollkaemper (eds), New Perspectives on the Divide between National and International Law (2007) 251, at 266–267.
  20. See on this in more detail Raffaela Kunz, Judging International Judgments Anew? The Human Rights Courts before Domestic Courts, European Journal of International Law 30 (2019), 1129–1163.
  21. ICJ, Jurisdictional Immunities of the State (Germany v. Italy: Greece intervening), Judgment of 3 February 2012, I.C.J. Reports 2012, p. 99.
  22. See on this stalemate Valentina Volpe, Anne Peters and Stefan Battini (eds), Remedies against Immunity? Reconciling International and Domestic Law after the Italian Constitutional Court’s Sentenza 238/2014 (Berlin/Heidelberg: Springer 2021).
  23. Supreme Court (Argentina) 368/1998 (34-M)/CS1, Ministerio de Relaciones Exteriores y Culto s/ informe sentencia dictada en el caso ‘Fontevecchia y D’Amico v. Argentina’ por la Corte Interamericana de Derechos Humanos, 14 February 2017, 340:47.
  24. Constitutional Court (Russia), Case no. 21-P/2015, 14 July 2015.
  25. See also Palombino, ‘Compliance with International Judgments: Between Supremacy of International Law and National Fundamental Principles’, 75 Za RV (2015) 503; Battini, E costituzionale il diritto internazionale?’, 3 Giornale di diritto amministrativo (2015) 367; Peters, ‘Supremacy Lost: International Law Meets Domestic Constitutional Law’, 3 Vienna Online Journal on International Constitutional Law (2009) 170.
  26. See e.g. Mikael Rask Madsen, Pola Cebulak and Micha Wiebusch, ‘Backlash against International Courts: Explaining the Forms and Patterns of Resistance to International Courts’, 14 International Journal of Law in Context (2018) 197.
  27. See already Kunz, EJIL, 1157, and Krisch, ‘Pluralism in International Law and Beyond’, in J. d’Aspremont and S. Singh (eds), Fundamental Concepts for International Law: The Construction of a Discipline (2019) 691.
  28. Higgins, ‘National Courts and the International Court of Justice’, in M. Adenas and D. Fairgrieve (eds), Tom Bingham and the Trasnsformation of the Law: A Liber Amicorum (2009) 405, at 417.
  29. See on this already Kunz 2020, 1157
  30. Case concerning Certain German Interests in Polish Upper Silesia, PCIJ Ser. A No. 7, p. 19.
  31. See, for example, ILC, Second Report on the Identification of Customary International Law, Michael Sir Wood, Special Rapporteur, UN Doc. A/CN.4/672, para 34; P. M. Moremen, ‘National Courts Decisions as State Practice: A Transjudicial Dialogue?’, North Carolina JIL32 (2006), 259; W. Friedmann, ‘The Use of ‘General Principles’ in the Development of International Law’, AJIL 57 (1963), 279.
  32. Daniel Peat, Comparative Reasoning in International Courts and Tribunals (Cambridge University Press 2019), 51.
  33. Peat, D. (2019). Domestic Law in the Jurisprudence of the International Court of Justice. In Comparative Reasoning in International Courts and Tribunals (Cambridge Studies in International and Comparative Law, pp. 49-82). Cambridge: Cambridge University Press. doi:10.1017/9781108233828.003, 3.
  34. See on this in detail Peat, D. (2019). In Comparative Reasoning in International Courts and Tribunals, Cambridge: Cambridge University Press. doi:10.1017/9781108233828.006
  35. ECtHR, Implementation of the judgments of the European Court of Human Rights: a shared judicial responsibility?, Background paper, Dialogue between judges, 31 January 2014, available at See on this Gerards, J., The European Court of Human Rights and the national courts: giving shape to the notion of ‚shared responsibility‘, in Gerards, J. and Fleuren, J. (eds.), Implementation of the European Convention of Human Rights and of the judgments of the ECtHR in national case- law (Cambridge: Intersentia 2014), 13–93.
  36. See the Dissenting Opinion of Judge Pinto de Albuquerque in the case of Hutchinson v The United Kingdom, App No. 57592/08 (ECtHR, 17 January 2017), at para 38.