Encyclopedia of Private International Law
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Encyclopedia of Private International Law

Edited by Jürgen Basedow, Giesela Rühl, Franco Ferrari and Pedro de Miguel Asensio

The role and character of Private International Law has changed tremendously over the past decades. With the steady increase of global and regional inter-connectedness the practical significance of the discipline has grown. Equally, so has the number of legislative activities on the national, international and, most importantly, the European level. With a world-class editor team, 500 content items and authorship from almost 200 of the world’s foremost scholars, the Encyclopedia of Private International Law is the definitive reference work in the field. 57 different countries are represented by authors who shed light on the current state of Private International Law around the globe, providing unique insights into the discipline and how it is affected by globalization and increased regional integration. The Encyclopedia consists of three inter-linked pillars, enhanced by sophisticated search and cross-linking functionality. The first pillar consists of A-Z coverage of the scope and substance of Private International Law in the form of 247 entries. The second pillar comprises detailed overviews of the Private International Law regimes of 80 countries. The third pillar presents valuable, and often unique, English language translations of the national codifications and Private International Law provisions of those countries. This invaluable combination represents a powerful research tool and an indispensable reference resource.
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Chapter P.16: Public international law and private international law

Alex Mills

I. Introduction

The relationship between public and private international law is a topic which has long been debated, and which remains controversial. Many modern private international lawyers would doubt that any deep relationship exists between the two subjects. At least formally, rules of private international law are often considered to be ordinary rules of national law, or even rules of national procedural law, made by national courts or legislatures. There is significant variation between the rules of private international law adopted in different states, and it would be very difficult to argue that, at least under current international law, any particular rules of private international law are mandated (with the possible exception of a state’s exclusive authority over questions of title to its land).

It is true, of course, that rules of private international law may be (and perhaps increasingly are) harmonized through treaties, and thus take the form of rules which are part of and governed by public international law, including its rules on the formation, validity and interpretation of treaties. Such treaties are commonly negotiated under the auspices of an international organization, the →Hague Conference on Private International Law (discussed further below), but may also be established by regional organizations as part of economic integration efforts. The Brussels Convention (Brussels Convention of 27 September 1968 on jurisdiction and the enforcement of judgments in civil and commercial matters, [1972] OJ L 299/32, consolidated version, [1998] OJ C 27/1; →Brussels I (Convention and Regulation)), Rome Convention (on the law applicable to contractual obligations (consolidated version), [1998] OJ C 27/34; →Rome Convention and Rome I Regulation (contractual obligations)) and →Lugano Convention (of 30 October 2007 on jurisdiction and the recognition and enforcement of judgments in civil and commercial matters, [2007] OJ L 339/3) are European illustrations of this practice – while the former two Conventions have now been replaced with European Regulations, the Lugano Convention is essentially designed to apply to non-EU Member States, and thus continues to function as a separate treaty. There are numerous other examples of such practices around the world, including the Protocol of Las Leñas (of 27 June 1992 on Judicial Cooperation and Assistance in Civil, Commercial, Labour and Administrative Matters, 2145 UNTS 421) and the Protocol of Buenos Aires (on International Jurisdiction in Contractual Matters, signed on 5 August 1994, available at <www.sice.oas.org/trade/mrcsrs/decisions/AN0194_e.asp) adopted by Mercosur in South America. Where such treaties are not directly enforceable as a matter of national constitutional law (→Constitutional law and private international law), national rules may also be necessary in order to implement the public international law obligations of the state. In any case, states may thus owe obligations of private international law to each other as a matter of public international law. It is further possible that, for example, the International Court of Justice might be seized with a dispute concerning the interpretation of a private international law treaty. This indeed occurred in relation to a dispute between →Belgium and →Switzerland regarding the →Lugano Convention, submitted to the ICJ in 2009, although the proceedings were discontinued in 2011. But no particularly deep connection between public and private international law is necessarily established through these possibilities or practices. A treaty harmonizing national rules of contract law would not make contract law ‘international’ in character – the international harmonization of private international law through treaties does not, on its own, give private international law a distinct character from other rules of national law.

A stronger connection between public and private international law is suggested through the central role played by the doctrine of →comity in private international law. Rules of private international law are at least partially based around ideas of respectful relations between states. A state should only impose its law or exercise its judicial authority in relation to a p. 1449dispute where it has a ‘legitimate’ claim to do so; otherwise the proper course of action, motivated by comity, is to defer to another court’s jurisdiction, apply another state’s law, or recognize and enforce the judgment of another state. Scholars and national courts frequently refer to the concept of comity as a motivating force behind private international law, but the classic definition that it is ‘neither a matter of absolute obligation, on the one hand, nor of mere courtesy and goodwill, upon the other’ (Hilton v Guyot 159 US 113, 163–4 (1895)) captures its inherent ambiguity or tension. The term comity is generally used to suggest that these principles of deference and respect are not required as part of public international law, even if they are more than a matter of courtesy, thus again suggesting (although not without ambiguity) that there is only a shallow connection between public and private international law.

This entry explores the contention that the connections between public and private international law are deeper than the above would suggest. It examines the historical relationship between the two areas of law, their overlap in terms of regulatory function, and an increased openness within both disciplines to the possibility of a connection between them. In so doing, it examines a range of ways in which public and private international law are mutually influential.

II. A brief history of public and private international law

The earliest origins of private international law are generally considered to be around the time of the Italian renaissance – a time when an expansion of international trade and commerce led to an increase in disputes with significant foreign elements (→Private International Law, history of). The idea of private international law emerged to respond to these problems, as a mechanism to address the risk of conflicting legal treatment of private disputes, while accepting a degree of pluralism in substantive private law. Private international law rules were developed as a distinct part of the universal natural law, ‘secondary’ norms which facilitated and supported the existence of diverse local legal systems by coordinating legal diversity. Private international law was thus first conceived of not as part of the local law which differed from city-state to city-state, but as part of a universal (natural) international law system – the ‘law of nations’ – which encompassed the modern territory of both public and private international law.

This idea of private international law has sustained and defined the discipline throughout most of its history. Under the statutist approach (→Unilateralism), perhaps the earliest idea of private international law, the potential for conflict between legal systems was addressed by attempting to develop a principled and analytical way of determining the scope or the effect of different laws. This was based on the idea that each statute ‘naturally’ belongs to one of two categories of laws, either ‘personal’ or ‘territorial’. The distinction between these types of laws was intended to reflect a natural division operating in all legal systems, thus again conceiving of private international law as part of a universal and international system of law.

Later scholars adopted different methods of defining this distinction, variously emphasizing the importance of territorial or personal characteristics, while retaining the essentially internationalist character of the discipline. The two dominant 19th century figures in private international law, at least outside the Anglo-American tradition, may be singled out as influential archetypes. In the early 19th century, the German scholar Savigny (→Savigny, Friedrich Carl von) rejected the statutist focus on the characterization of the laws themselves, arguing for an account of private international law in which the basic unit of analysis is the ‘legal relation’. For Savigny, the role of private international law was thus to find the law to which each relation ‘belongs’, to ‘ascertain the seat (the home) of every legal relation’. It is central to Savigny’s approach that the private international law rules he developed were higher level, universal norms – part of an international system of law, derived from the fact of a community of territorial states.

The Italian scholar and political figure Mancini, (→Mancini, Pasquale Stanislao) working later in the 19th century, shared much of Savigny’s approach, but adopted →nationality as the founding concept and the key determinant in attributing regulatory authority to states. This was based on a conception of the nation as founded on personal connections (embodying the people and their history and culture) rather than territorial power. On the basis of this approach, Mancini argued that the applicable law in a private international law dispute should (generally) be determined by the p. 1450nationality of the parties. Like Savigny, Mancini viewed private international law rules as ‘secondary norms’ which are essentially part of a broader system of law – in his case, the law of a community of nations rather than Savigny’s community of territorial states. In both cases, rules of private international law were essentially characterized as serving an international function of global ordering or governance, coordinating relations between different legal orders.

This close relationship between public and private international law, viewed as integral parts of a broadly defined ‘law of nations’, faded in both theory and practice over the course of the 19th century. By the end of the 19th century, there was an increasing view that rules of private international law were not inherent parts of international law, because international law was concerned only with the ‘public’ relations between states. This theoretical development corresponded with an increased diversity of private international law rules in practice (partly prompted by divisions over the use of ‘nationality’ as a connecting factor), which made the view of private international law as fundamentally international in character increasingly seem untenable. In federal systems, such as the United States (→USA), the analysis and development of private international law increasingly focused on problems arising within the system, involving its constituent states. Their resolution increasingly drew on national policies and constitutional concerns, and a lack of distinction between the interstate and foreign contexts shifted the focus away from the traditional ‘international’ perspective on private international law.

In response and reaction to these developments, a series of Hague Conferences on Private International Law were held between 1893 and 1904, to work towards the harmonization of private international law (→Hague Conference on Private International Law). While these conferences had only limited success, they were nevertheless greatly significant in maintaining the idea that private international law was a subject which should be dealt with at the international level. The tradition of internationalism which they established was the direct antecedent of the Hague Conference on Private International Law, founded as an international institution in 1955.

III. Functional and doctrinal connections between public and private international law

In the early parts of the 20th century, the idea that public and private international law were entirely separate disciplines appeared to become established. This was a product both of a narrowing of the domain of public international law, to exclude ‘private’ actors and their relations, and of the reconceptualization of private international law itself as national law. This theoretical separation has, however, tended to mask a range of functional connections between the two subjects, which have long been evident to practitioners whose work has cut through the artifice of academic disciplinary boundaries. The rules of public international law include rules of ‘jurisdiction’, which determine the permitted scope of a state’s exercise of regulatory authority (→Jurisdiction, foundations). A state may, for example, criminalize conduct in its territory, or the conduct of its nationals outside its territory. Each act of regulation must be justified by one of the accepted grounds of jurisdiction in order to comply with public international law. Because of the exclusion of ‘private’ concerns from public international law, doubts have sometimes been expressed as to whether these rules apply to private law regulation or disputes. There is, however, little in principle to support such a distinction. Rules of private law are exercises of ‘public’ governmental authority as much as rules of criminal law, and they are ultimately sanctioned through coercive judicial and executive powers. If a court orders that a party is liable to pay →damages or face seizure of their property because they have breached tort law, this is not characteristically different from an order that they are liable to pay a fine or face seizure of the same property because they have breached criminal standards. The ultimate recipient of the penalty may differ, but the state power which is exercised to compel payment does not. Public and private law remedies indeed often overlap, and may be interchangeable. In different legal systems, different approaches may notably be taken to regulating particular issues – for example, competition law may be approached through public or private enforcement, or a combination of both. The distinction between public and private law has long been criticized as a legal artifice, and in any case does not p. 1451appear materially relevant to the question of whether state regulatory power is implicated. A state’s contract law, no less than its criminal law, pursues national policy objectives. Public international law scholarship has, in recent years, re-opened its attention to a range of matters traditionally characterized as ‘private’ and thus as falling outside the scope of the discipline, recognizing that they have important ‘public’ governance implications and effects.

The recognition that public international law rules of jurisdiction apply to matters of private law reveals a functional commonality between public and private international law rules. Both impose limits on the circumstances in which a state may assert its regulatory authority over a particular person, relationship or event. Public international law establishes that a state may not impose its regulation in the absence of a recognized justification, but does not (at least generally) mandate that state regulation be imposed where such a recognized justification exists. Principles of ‘access to justice’, developing particularly in the context of human rights law (→Human rights and private international law), may in future have an increased role in requiring states to expand their grounds of civil jurisdiction, but at present they have had a limited influence. The implication of this is that there is a great deal of scope for different rules of private international law to function compatibly with public international law. Public international law defines the outer limits within which national rules of private international law must operate. Those national rules are then an implementation of both public international limits, and, within those limits, national policies concerning matters of private international law. This is not to say that private international law is ‘subsumed’ by public international law. Private international law has its own policy concerns and interests, which operate within the public international law framework. The rules of private international law are also some of the strongest evidence of what states view as accepted grounds of public international law jurisdiction, and what they view as ‘exorbitant’. Private international law sources were indeed historically one of the strongest influences on the development of public international law jurisdictional rules. The functional commonality between the two disciplines highlights the importance of recognizing that they are in a relationship of mutual influence. Private international law rules are shaped by rules of public international law, but rules of public international law are also shaped by the practices of states in the context of private international law.

An additional distinct influence of public international law on private international law may be observed in the development of rules of →public policy (ordre public), as a defence against the recognition and enforcement of a foreign judgment, or an exception from the application of foreign law (→Foreign law, application and ascertainment). Public policy is the means through which states may determine that other policy considerations outweigh those of private international law itself – that the usual obligations to recognize a foreign judgment or apply a foreign law are trumped by the harm which would be caused in doing so in the particular circumstances, because the judgment or law offends against important principles of domestic law. For this reason, however, public policy must be construed narrowly, otherwise it would risk undermining private international law altogether – a foreign judgment or law must not be rejected simply because it is different, but only where that difference is fundamentally objectionable. Different considerations apply, however, where the public policy concerned is not derived from national interest, but from public international law such as international human rights law – sometimes referred to as ‘truly international’ public policy. In these circumstances, the application of public policy is not a projection of one state’s norms on matters which would otherwise be governed by the other state, but rather a recognition and enforcement of norms which bind both states. National courts have rightly suggested that they should be readier to apply public policy in such circumstances – for example, refusing to apply Iraqi law which purported to nationalize property seized in the 1990 invasion of Kuwait, contrary to the UN Charter and resolutions of the Security Council (Kuwait Airways v Iraqi Airways [2002] UKHL 19). In such cases, giving effect to norms of international law by refusing to apply foreign law or recognize a foreign judgment essentially involves prioritizing other rules of public international law over the rules of ‘jurisdiction’ which provide the foundations of private international law (→Private International Law, foundations) – but such a prioritization may well be demanded by public p. 1452international law itself. In any case, an internationalized public policy does not challenge the connection between public and private international law, but rather strengthens it.

A further element to the ‘internationalism’ of private international law may be found in its policy objectives. As noted above, private international law has its own policy concerns and interests. Like public international law, it governs the allocation of regulatory authority between states, relying traditionally on territorial or personal connections to justify regulation. But within the discipline of private international law, there are also policy goals which relate to how this regulation should function. Rules of private international law have traditionally (through choice-of-law rules in particular) sought to achieve objectives of decisional harmony, ensuring that the same decision is reached wherever in the world a dispute is litigated. Together with rules limiting overlapping jurisdiction and requiring the recognition and enforcement of foreign judgments, this minimizes the risk that parties may be subject to inconsistent regulation, leading to potentially conflicting exercises of state enforcement powers. Another related principle is that incentives and opportunities for forum shopping should be reduced (through both choice-of-law rules and jurisdictional rules), and thus litigation should take place in the most appropriate forum rather than the forum which most favours the claimant – risking again parallel proceedings and inconsistent regulation, as well as inefficient dispute resolution. To put these policy goals another way, private international law has long been concerned, among other things, with coordinating the peaceful coexistence of sovereign states, by striving to reduce the ‘conflict of laws between them’.

These are not objectives which can be reached by each state acting unilaterally in adopting its own national rules of private international law, in pursuit of its own policies. They require a process of formal or informal coordination, the recognition by states that they have collective interests and goals which may be best served through rules of private international law which are, at least to some extent, internationally harmonized. This ‘internationalist’ perspective on private international law is exemplified by the work of the Hague Conference on Private International Law. According to this tradition, part of the function of rules of private international law is fundamentally ‘public’ and ‘international’ in character – it has at least a relationship of functional equivalence to the global governance ambitions of public international law. Similar ‘public’ functions of private international law rules may be observed in federal or similar systems in which private international law rules serve the function of ordering the distribution of regulatory authority, a role which private international law has increasingly played in the European Union, →Australia and →Canada. While as noted above these developments have in the past discouraged thinking about private international law from an international perspective (by instead increasing focus on such issues as they arise within the federal system), ironically they illustrate the way in which private international law might be applied to achieve public, systemic objectives, closely aligned to those of public international law. An internationalist vision of the character and objectives of private international law has been strongly influential in the history of the discipline, and could well remain central to its future.


  • Adrian Briggs, ‘The Principle of Comity in Private International Law’ (2012) 354 Rec. des Cours 65;

  • Stéphanie De Dycker, ‘Private International Law Disputes before the International Court of Justice’ (2010) 1 JIDS 475;

  • Edward Hambro, ‘The Relations Between International Law and Conflict Law’ (1962-I) 105 Rec. des Cours 1;

  • Erik Jayme, Internationales Privatrecht und Völkerrecht (CF Müller 2003);

  • Stefan Leible and Matthias Ruffert (eds), Völkerrecht und IPR (Jenaer Wissenschaftliche Verlagsgesellschaft 2006);

  • Andreas F Lowenfeld, ‘Public Law in the International Arena: Conflict of Laws, International Law, and Some Suggestions for Their Interaction’ (1979-II) 163 Rec. des Cours 311;

  • Campbell McLachlan, ‘The Influence of International Law on Civil Jurisdiction’ (1993) 6 Hague Yrbk Intl L 125;

  • Francis A Mann, ‘The Doctrine of Jurisdiction Revisited After Twenty Years’ (1984-III) 186 Rec. des Cours 19;

  • Pierre Mayer, ‘Droit international privé et droit international public sous l’angle de la notion de compétence’ (1979) 68 Rev.crit.DIP 1, 349 and 537;

  • Ralf Michaels, ‘Public and Private International Law: p. 1453German Views on Global Issues’ (2008) 4 J Priv Int L 121;

  • Alex Mills, ‘Rethinking Jurisdiction in International Law’ (2014) 84 BYIL 187;

  • Alex Mills, The Confluence of Public and Private International Law (CUP 2009);

  • John R Stevenson, ‘The Relationship of Private International Law to Public International Law’ (1952) 52 Colum.L.Rev. 561;

  • Pascal de Vareilles-Sommières, La Compétence Internationale de L’État en Matière de Droit Privé (LGDJ 1997);

  • Ben Atkinson Wortley, ‘The Interaction of Public and Private International Law Today’ (1954-I) 85 Rec. des Cours 237.