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Max Planck Encyclopedia of Public International Law [MPEPIL]

Unification and Harmonization of Laws

Martin Gebauer, Felix Berner

Content type:
Encyclopedia entries
Product:
Max Planck Encyclopedias of International Law [MPIL]

Module:
Max Planck Encyclopedia of Public International Law [MPEPIL]
Article last updated:
August 2019

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2023. All Rights Reserved.date: 25 April 2025

Subject(s):
International co-operation

Published under the auspices of the Max Planck Institute for Comparative Public Law and International Law under the direction of Professor Anne Peters (2021–) and Professor Rüdiger Wolfrum (2004–2020). 

A.  Concept, Development, and Institutions

1  Unification or harmonization of laws can be achieved on very different levels, and by very different means. The evolution of the common law in English legal history, for example, can be regarded as a process of unification. To a certain degree, the reception of the ius commune throughout the European continent, starting at the end of the Middle Ages, unified the application of the law as well. The ius commune, however, never replaced the local laws but applied subsidiarily. As a consequence, the idea of a national codification was not born in England, but on the European continent. Starting from the age of enlightenment, many codifications spread over the world. One of the main goals these codifications tended to achieve was the unification of laws on a national level. But there was a price to pay. The former unity in legal reasoning, language, and education vanished by entrusting the development of the law to national legislators, courts, and writers.

2  The idea of unification on an international level arose with the awareness of diversity, at a time when the law had finally come to be considered national in character. In the second half of the 19th century, it was enthusiastically proposed to unify private laws across national borders by means of international treaties. In 1874, Pasquale Stanislao Mancini voted for the unification of substantive rules in the field of maritime and commercial law, and in other fields of law he proposed the unification of private international law. The Institut de Droit international, which had been founded one year before, later followed him in that proposal. Others believed in the possibility to create a world-law (Zitelmann). The very early international conventions which entered into force regarded the protection of industrial property (Convention for the Protection of Industrial Property [1883]), and the protection of intellectual property (Convention for the Protection of Literary and Artistic Works [1886]) (Industrial Property, International Protection; Intellectual Property, International Protection).

3  In 1893, the Hague Conference on Private International Law was founded. Ever since, this institution has promulgated a large number of international conventions and today is still regarded as one of the most important organizations for the unification and harmonization of private international law on the world-wide stage. Others are the International Institute for the Unification of Private Law (UNIDROIT) founded in 1926, the United Nations Commission on International Trade Law (UNCITRAL) established in 1966–67, and the International Commission on Civil Status (ICCS). In addition, there are regional organizations, like the European Union (‘EU’) (European [Economic] Community; European Union, Historical Evolution), which can not only play an important role on a regional basis, but also influence the unification process on the world-wide level. The EU acceded to the Hague Conference in 2007.

4  The enthusiasm of the early years has been replaced during the 20th century by a more pragmatic view about the advantages and the costs of unifying the law at the international level. Moreover, other methods and instruments concerning the harmonization of private law issues have been developed. As to the difference between unification on the one hand and harmonization of laws on the other, it can be regarded as a matter of degree. Unification is concerned with the creation of identical rules, whereas harmonization tends to produce more or less similar law in different countries.

B.  Subject-Matter Covered by Unification and Harmonization

5  Nearly every subject matter of private and commercial law has at least been touched by efforts of unification or harmonization at the international or regional level. A first distinction must be drawn between the unification of the internal substantive laws of the various countries on the one hand, and the unification of private international law on the other. By unifying the conflict rules of private international law, it can be ensured that a case containing a foreign element results in the application of the same national substantive rules, irrespective of the country where the action is brought.

6  Very successful projects of unification or harmonization on the world-wide stage, regarding conflict or substantive rules, are the numerous Hague Conventions on Private International Law and on International Civil Procedure; the Conventions on the International Carriage of Persons or Goods by Aircraft, by Sea or by Road; the 1958 Convention on the Recognition and Enforcement of Foreign Arbitral Awards (‘New York Convention’); the 1985 UNCITRAL Model Law on International Commercial Arbitration (UN Doc A/40/17, Annex I, amended in 2006, UN Doc A/61/17, Annex I); the 2004 UNIDROIT Principles of International Commercial Contracts (first edition published in 1994, last amended 2016 <https://www.unidroit.org/> [18 September 2020]); and finally, the 1980 United Nations Convention on Contracts for the International Sale of Goods (‘CISG’) (see also Commercial Arbitration, International; Commercial Contracts, UNIDROIT Principles).

7  The CISG is probably the most influential instrument of unification. It applies to international sale of goods cases in more than 90 countries. And apart from its immediate application, it affected and still affects numerous national legislators in their efforts to reform the law of obligations. The Convention entered into force in 1988 and was drafted by UNCITRAL, but the history of the CISG goes back to the year 1929 and started with UNIDROIT and the comparative works of Ernst Rabel on the sale of goods.

8  An important yet disappointing example of a much scaled-down unification project were the efforts undertaken over more than a decade for the creation of a world-wide Hague Convention on International Jurisdiction and Foreign Judgments. Ultimately, it did not completely fail but it was reduced to the 2005 Hague Convention on Choice of Court Agreements, which entered into force on 1 October 2015. It remains to be seen whether the Convention on the Recognition and Enforcement of Foreign Judgments in Civil or Commercial Matters (concluded 2 July 2019; <https://www.hcch.net/> [24 June 2020]) will be a more successful project.

9  Closely connected to the subject matter covered by the single unification project are the range of the unified law and its scope of application. Does it apply only to international matters or to internal cases as well? And if it does apply only to cross-border cases, is it necessary that the other country is a contracting or a Member State as well? The answer to these questions is relevant to the remaining importance of the internal law beside the unified law. The CISG, for example, applies only to contracts between parties whose places of business are in different States. As a consequence, contracts between parties having their places of business within the same State are not governed by the unified law of the CISG. They are governed by national law.

10  The second question, as to the connection of a foreign State to the uniform law, becomes relevant mainly for the application of unified conflict rules in private international law. In the EU, for example, the conflict rules on the law applicable to contractual and to non-contractual obligations have been unified by the so-called Rome I and Rome II Regulations in 2007 and 2008. Both regulations find universal application in the sense that any law specified by these regulations shall be applied whether or not it is the law of a Member State (loi uniforme). The same is true for the Rome III Regulation, the EU Succession Regulation, and the EU Regulations on Matrimonial Property Regimes and Property Consequences of Registered Partnerships. This application of EU law in cases containing a foreign element from a third State leads to a complete replacement of any domestic conflict rule within the subject matters covered by the regulations. Within the scope of the regulations, domestic conflicts law of the Member States no longer exists. This kind of unification is complete in that it avoids the parallel existence of unified and non-unified law.

C.  Various Methods and Approaches concerning Unification and Harmonization

1.  Unification by Treaty

11  The classical form which was preferred in the early days of unification, and still today plays an important role, is the treaty (Treaties). The Parties, after having reached agreement on the text and completed the ratification process, have to ensure the application of the uniform law throughout their territories. The treaty may be bilateral or multilateral in character, it may create a universal convention open for accession to any State, or just a regional convention open for accession only to a limited number of States. The treaty, however, is inflexible in that later changes and adaptations of the conventional rules are difficult to realize, and sometimes even impossible. Moreover, the uniform law created by treaties at diplomatic conferences tends to be fragmentary and is always surrounded by a sea of non-unified laws.

2.  Unification and Harmonization by Supranational Law

12  Where single States have transferred legislative powers to a supranational organization like the EU, some of the difficulties provoked in the unification process by treaties can be avoided. Over recent decades, EU private law has been created mainly by means of regulations and directives. The regulation is binding in its entirety, and directly applicable in all Member States. The directive, by contrast, is binding as to the result to be achieved, upon each Member State to which it is addressed, but leaves to the national authorities the choice of form and methods. By leaving to the national legislators the choice of form and methods, the directive is, at least in theory, an instrument of harmonization whereas the directly applicable regulation leads to full unification. Nevertheless, directives can also require maximum (or full) harmonization and therefore lead, at least partly, to an indirect unification. Harmonizing directives have been used, for example, in the fields of general contract and consumer law to achieve the objectives of EU law without completely replacing the existing systems of private law in the Member States (European Union Law and Domestic [Municipal] Law). Regulations, on the other hand, have been used to unify the European law of civil procedure and European private international law by partly replacing the pre-existing systems of the Member States in these fields.

13  The unified or harmonized EU private law is quite easy to change or revise compared with a convention concluded by a number of States. And the range of unification can be longer if a complete set of pre-existing national rules is replaced by supranational law as was the case in essential parts of private international law. As a consequence, supranational law is frequently less fragmentary than the law unified by international treaties. A third advantage of unification and harmonization by supranational law lies in the fact that within a supranational organization it is easier to entrust a common judicial body with the autonomous interpretation of uniform law (see paras 25–29 below).

3.  Harmonization by Means of Autonomous Reception, Model Rules, and Principles

14  A national legislator planning to reform a branch of law is well advised to look at the solutions offered by foreign legal orders. The reception of convincing models and the transplantation of legal institutes have played an important role in legal history and in present times. Quite often, convincing solutions of a legal problem are not only offered by foreign domestic law, but by modern uniform law instruments. Taking again the example of the CISG, many legislators have been inspired by this uniform law instrument, like the Chinese legislator in drafting a national contract law, or the European legislator in drafting the sales directive. Certainly this kind of reception and extension to domestic law leads to harmonization on the international level. But it has nothing to do with the binding character of the CISG because it works outside the scope of the Convention. Autonomous reception can be regarded as a consequence of the fragmentary yet, in its contents convincing, character of the uniform law created by international treaties.

15  Beside this kind of a more or less spontaneous reception of uniform law by means of an autonomous harmonization outside the scope of the specific uniform law, there are soft law instruments which are created precisely in order to be adopted in a flexible way. An important example of a very influential model law is the 1985 UNCITRAL Model Law on International Commercial Arbitration—as amended in 2006. The harmonizing effect of model laws differs from unification by means of international treaties, in that a State adopting a model law is free to modify the text at any time, or to adopt it only in part. Like the autonomous reception and extension of binding uniform law, the adoption of a model law has the consequence of a lower degree of unity compared with the binding effect of a convention within its scope. It offers, however, a certain degree of similarity. And at the same time it is much easier to be agreed upon because of its flexibility.

16  The UNIDROIT Principles of International Commercial Contracts (1994, 2004, 2010, and 2016) represent another example of soft law with great impact. This set of rules contains a general part of contract law, and differs from model laws in that it is not only addressed to legislators—even if the UNIDROIT Principles have been used, like the CISG, by many legislators as a source of inspiration. The UNIDROIT Principles play an important role, as applicable law, in international commercial arbitration. Finally, the UNIDROIT and the American Law Institute Principles of Transnational Civil Procedure (2004) serve as a tool both for domestic legal reform and in international dispute resolution.

D.  Unification and Harmonization within the European Union

17  As already mentioned above (see para. 12), Union private law has been created mainly by means of regulations and directives, ie secondary EU law. But from the very start, the then Treaty establishing the European Community (‘EC Treaty’) contained rules concerning antitrust law and the fundamental freedoms, which do have a strong impact on private law branches like company law (Antitrust or Competition Law, International; Human Rights). And beside primary and secondary Community law, the unification of certain topics was entrusted to negotiation[s] among the Member States. According to the former Art. 293 EC Treaty (ex Art. 220), such negotiations included, inter alia, ‘the simplification of formalities governing the reciprocal recognition and enforcement of judgments of courts or tribunals and of arbitration awards’. In 1968, the Member States entered into the Convention on Jurisdiction and the Enforcement of Judgments in Civil and Commercial Matters, which came into force in 1973 (‘Brussels Convention’). It was one of the most successful unification instruments ever launched in Europe, and it went beyond Art. 293 EC Treaty in that it contained not only rules on the recognition and enforcement of foreign judgments, but on adjudicatory jurisdiction as well. Later, the parallel Convention on Jurisdiction and the Enforcement of Judgments in Civil and Commercial Matters (‘Lugano Convention’) was concluded with the States of the European Free Trade Association (EFTA). Following the same method, unification by means of a treaty, the Member States in 1980 created the Convention on the Law Applicable to Contractual Obligations (‘Rome Convention’).

18  Today, unification of private law by conventions no longer plays an important role within the EU. The Lugano Convention with the EFTA States, however, was revised in 2005. But both the Brussels and the Rome Conventions were succeeded by regulations, due to an important revision of the then EC Treaty. The Treaty of Amsterdam, which entered into force in 1999, authorized the adoption of Community measures—thus including both regulations and directives—in civil matters with cross-border implications in order to realize the ‘area of freedom, security and justice’ (Art. 1 (3)). In the following years, a great number of regulations entered into force concerning not only matters of civil procedure, but also of private international law, including family law provisions. After the Lisbon Treaty entered into force, the legal basis for such regulations has been Art. 288 (2) Treaty on the Functioning of the European Union (‘TFEU’).

19  As to the subject-matter of substantive private law, unification and harmonization within Europe started in the fields of company law, industrial property, intellectual property, competition law, employment law, and with the enactment of many consumer-protecting directives it spread over to general contract law. Today, the private law systems of the Member States are pervaded by Community law. Since harmonization in the central parts of private law worked on a fragmentary step-by-step approach and the various directives were not harmonized among each other, the coherence of the private law system within the Member States was seriously challenged. New methodological problems arose, like the interpretation of domestic law in conformity with directives (see para. 29 below).

20  The European Commission’s Action Plan on a More Coherent European Contract Law of 2003 called for the elaboration of a ‘Common Frame of Reference’ (‘CFR’). By this time, the Principles of European Contract Law (‘PECL’), an important soft law instrument similar to the UNIDROIT Principles but more closely linked to Europe, had recently been published (Parts I and II in 1999; Part III in 2003). The PECL had been prepared by the Commission on European Contract Law over two decades. The preparation of the CFR was now entrusted to a network, mainly consisting of the Study Group on a European Civil Code (‘Study Group’) and the Research Group on EC Private Law (‘Acquis Group’). The first academic Draft Common Frame of Reference (‘DCFR’) was based in part on a revised version of the PECL and published in 2008. The publication of the final academic CFR followed one year later in 2009. The DCFR in turn provided the basis for a Proposal for a Regulation of the European Parliament and of the Council on a Common European Sales Law. This proposal however has not been adopted.

E.  Application and Interpretation of Unified and Harmonized Laws

1.  Interplay between Harmonized and Non-Harmonized Laws

(a)  Limited Scope of Application and Gaps

21  The early enthusiasts believed that the international unification of substantive private law would always make it easier to resolve legal problems of transnational activities, and that uniform law could even render superfluous the techniques of private international law and the application of foreign domestic law. During the 20th century it became clear, however, that no branch of private law has ever been unified in a complete way on the international level, and that it is a difficult task to do so even on a regional level. Due to the gaps within uniform law, and due to its fragmentary character, and its limited scope of application, uniform law in many cases seems like an island within the sea of non-unified rules. In legal practice, it is exceptional that a case is governed exclusively by an instrument of uniform law. At least in a subsidiary way, domestic rules often have to be taken into account and applied according to the forum rules of private international law.

22  Uniform law instruments sometimes contain a specific provision on the interpretation and the filling of gaps. Art. 7 (2) CISG provides that ‘[q]uestions concerning matters governed by this Convention which are not expressly settled in it are to be settled in conformity with the general principles on which it is based’.

23  Such provisions are important and they aim to extend the regime of the uniform law instrument as far as possible if the gap is located within the scope of application. But at some point it becomes impossible to find a commonly acceptable solution within the uniform law’s own spirit. Consequently, Art. 7 (2) CISG continues to provide that, ‘in the absence of such principles, [those questions are to be settled] in conformity with the law applicable by virtue of the rules of private international law’.

(b)  Minimum and Full Harmonization

24  A specific example of the interplay between harmonized and non-harmonized laws is given when the harmonizing instrument aims to achieve, as far as possible, a certain substantive goal. The concept of the so-called minimum harmonization was until recently commonly used in European consumer law directives. Minimum harmonization provides only for a certain minimum level to be reached at least. But it leaves it open to go further in order to reach a higher standard of protection in domestic law—at the expense of unity. On the other hand, the so-called full harmonization aims to reach not a minimum but a uniform level. This approach of full harmonization now governs much of the European consumer law (see Directive 2011/83/EU of the European Parliament and of the Council of 25 October 2011 on Consumer Rights).

2.  Interpretation of Unified and Harmonized Laws

(a)  Uniform Interpretation

25  The interpretation of unified and harmonized laws differs from the interpretation of domestic law. Uniform law will lose its uniform character if a different meaning is given to the same rules in the various countries concerned. Already in the year 1930, Etienne Bartin mentioned the risk of a ‘déformation nationale des textes conventionnels’ (614). Art. 7 (1) CISG recalls that ‘[i]n the interpretation of this Convention, regard is to be had to its international character and to the need to promote uniformity in its application and the observance of good faith in international trade’.

26  Uniform interpretation of uniform law can be achieved only by paying attention to foreign decisions as well, even if foreign precedents do not have binding force. But they are to be taken into account with a comparative view, and at least the foreign precedents can have the force of a good argument. Each court applying the uniform law instrument has to make sure that the courts of other countries could reach, or have already reached, the same or similar results. Case digests and databases on the internet are very helpful in that regard.

(b)  Autonomous Interpretation and Judicial Authorities

27  Connected to uniform interpretation, yet not identical, is the autonomous interpretation of uniform and harmonized law. Autonomous interpretation does not proceed by reference to the meanings and particular concepts of a specific domestic law. It rather refers to the uniform law instrument’s own systems and objectives. A pre-contractual obligation arising out of culpa in contrahendo, for example, which under a certain domestic law is clearly to be qualified as a contractual obligation, may have to be characterized as a delict or tort under uniform law.

28  Both uniform and autonomous interpretation can best be achieved by entrusting an international or supranational court with the competence of interpreting uniform law. This is very difficult to achieve, however, for uniform law instruments that apply on a world-wide level like the CISG. It is much easier if unification and harmonization works on a regional level, like in the EU. The European Court of Justice (‘ECJ’) has developed, over recent decades, a wide range of autonomous concepts on private law issues (European Union, Court of Justice and General Court). According to the EU Treaty, the courts and tribunals of the Member States are empowered and in certain cases obliged to submit a question of interpretation regarding Community law to the ECJ.

(c)  Interpretation of Harmonized Laws within the European Community

29  Methodological questions of a specific kind arise where the law is not unified—by means of conventions or EU regulations—but harmonized by means of an EU directive. The directive does not find an immediate application on the ‘horizontal’ level between private parties. It rather requires implementation in the legal systems of the Member States. Sometimes, the domestic law of the Member States does not comply with the objectives of the applicable directive even after it has been implemented. But as far as possible, national courts are obliged by EU law to give an interpretation to domestic law which is in conformity with the directive. Since it is only the domestic law that finds immediate application—and the ECJ is not empowered to give an interpretation of the Member States’ domestic law—it is one of the most controversial questions within Community private law to what extent the courts of a Member State are empowered, or even obliged, to implement on their own the objectives of a directive by interpretation against the wording of domestic law.

F.  Assessment

30  The unification and harmonization of laws has a long history of both failed and successful projects. The general enthusiasm of the early days has gone. Today it seems clear that neither unity nor diversity of law can be regarded as such as objectives to be achieved. What seems necessary is a cost–benefit analysis in every branch of law on the specific needs for unification or harmonization. At the global level, successful measures have been taken by UNIDROIT and UNCITRAL in recent years in the trade-related private law areas of credit, finance, and securities, but also in general contract law, commercial arbitration, and transnational civil procedure. The most successful measures taken by the Hague Conference mainly regard the fields of private international law.

31  Attitudes have changed as to the methods and techniques. Unification by treaty still plays an important role since on the international level it can result in a high degree of certainty and predictability. But other forms of harmonization by soft law which have been developed over recent decades in certain branches seem to offer significant advantages. Soft law may be addressed to private parties or to legislators. Addressed to legislators it may even lead to ‘hard’ law on the domestic level. Model laws containing model rules and principles frequently offer a very high degree of quality for the means they are created by. Usually they are lacking the disadvantages of a ‘political’ creation that seems typical for international treaties.

32  As to subject-matter, the regional or global level of unification and harmonization can be of great importance. Matters of family or consumer law, for example, seem more appropriate for unification on a regional rather than on the global level. In the future, the general interplay and cooperation between the different regional and global levels will have to be taken into account more and more. In Europe, for example, a Eurocentric approach should be avoided in order to keep a connection with the world outside. This connection was challenged in recent years not only by regional enthusiasm about the creation of a new European private law, but also by the constitutional changes that minimized the Member States’ powers to legislate in the fields of private international law after the Treaty of Amsterdam. But the accession of the EU to the Hague Conference in 2007 was certainly a step towards improvement.

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