A.  Notion

1  When a State makes assurances to another subject of international law in a way that leads the other legitimately to place trust and confidence in the assurances, international law will in certain circumstances protect the expectations created (Subjects of International Law). States, in their relations with others, ‘should not be allowed to cause confusion and to disappoint legitimate expectations by blowing hot and cold’ (Lauterpacht [1944] 150); the protection of legitimate expectations is a concomitant of the general requirement that States must act in their mutual relations in good faith (bona fide). This is so because a State cannot, to the prejudice of another, be permitted to benefit from its own inconsistency. It is not surprising that international law should protect legitimate expectations; ‘[l]aw of every type relies on the fulfilment of expectations’ (Schwarzenberger [1955] 290).

B.  Historical Evolution

2  The term legitimate expectation or expectations (‘confiance légitime’ or ‘attentes légitimes’ in French) has long been a part of the lexicon of international law (Witenberg [1933] 532–33). Both the logic of legitimate expectations and the use of the term itself can be traced back to the 19th century. It nevertheless took time before the term would acquire the meaning it has come to have in the modern period.

3  The case Portendick (Great Britain v France) (1843) is an early example of the logic of legitimate expectations. France had assured Great Britain that it had no intention of closing the port of Portendick in French Senegal (at 640). France later closed the port; British ships duly suffered damage as a result. The British argument was to the effect that, France having made an official communication, Great Britain was justified by international law to give trust and confidence to the French declaration (at 641). The tribunal agreed with Great Britain: it determined that

Given France’s representation to Great Britain, France must act in a manner that did not disappoint the legitimate expectations to which France’s own conduct had given rise on the part of Great Britain (see also Jesse Lewis [United States] v Great Britain [1921] 92–93).

4  An early instance of the use of the terminology ‘legitimate expectations’ can be found in the General Report on the Declaration concerning the Laws of Naval Warfare. The General Report observed, in relation to Art. 65, which provided that the provisions of the Declaration were ‘an indivisible whole’, that ‘a legitimate expectation would be falsified if one Power might make reservations on a rule to which another Power attached particular importance’ (General Report on the Declaration concerning the Laws of Naval Warfare [1914] 142).

5  There is, similarly, a long tradition in international law for the protection of legitimate expectations of investors (de Nanteuil [2020] at 70). In the Aboilard Case (France v Haiti) the Haitian government had concluded concession contracts with a French investor. After having acted over a period of time in such a way as to give rise to expectations on the part of the investor, by giving him exclusive concessionary rights to certain utilities, the Haitian authorities purported to take the view that certain domestic law conditions had not been fulfilled; the investor’s concession was revoked. The tribunal held that the revocation amounted to an internationally unlawful act. Haiti had created ‘des attentes légitimes qui, ayant été trompées par le fait du gouvernement lui-même, ont entrainé un préjudice dont réparation est due’ (at 80 ‘legitimate expectations which, having been falsified by the Government itself, have led to harm for which reparation is due’ [translation by author]; see also Shufeldt [Guatemala v United States] [1930] 1094). The tribunal in Texaco v Libya suggested in a similar vein that, where a host State had made particular commitments to foreign investors that their position would be guaranteed or maintained, the commitments could give rise to legal obligations for the State (Texaco v Libya [1977] at 470).

6  The concept of legitimate expectations has come over time to acquire somewhat more fixed contours. It continues to be used in various contexts. It is encountered in inter-State relations governed by general international law, as well as in the context of investment protection, where the principle is a product of particular treaty instruments. It has, in both contexts, a close connection with the fundamental principle of good faith.

7  In general international law, the principle of legitimate expectations ‘stems from the general requirement that States act in their mutual relations in good faith and is designed to protect the legitimate expectations of a State that acts in reliance upon the representations of another’ (Chagos Marine Protected Area Arbitration [Mauritius v United Kingdom] [2015] para. 435; South China Sea Arbitration [Philippines v China] [Award on Jurisdiction and Admissibility] [2015] para. 250). As between States, legitimate expectations are protected through the operation of doctrines such as estoppel, acquiescence, and the binding effect of unilateral declarations (Declaration; Unilateral Acts of States in International Law).

8  The principle of legitimate expectations in the investment context, however, refers to the protection to which a foreign investor is entitled under the fair and equitable treatment clause (Fair and Equitable Treatment) to be found in investment treaties (McLachlan Shore and Weiniger [2017] 314; Forteau Miron and Pellet [2022] 1494–95). In both scope and refinement that protection goes further than under general international law (Kolb [2017] 243).

C.  Operation of Legitimate Expectations in International Law

9  The ways in which international law operates to protect legitimate expectations under general international law, by operation of eg estoppel, acquiescence, and the binding effect of unilateral declarations, are based on good faith. This would follow from the fact that, as the tribunal observed in Iraq v Turkey, the principle of good faith lays down a requirement for States to ‘act honestly, fairly, refrain from taking unfair advantage and to honour legitimate expectations’ (Iraq v Turkey [2023] para. 379). As one author observed, international law considers, on the basis of good faith, that ‘un comportement fait naître chez les autres Etats une attente légitime qui a certains effets de droit’ (‘a course of conduct may give rise to a legitimate expectation on the part of other States, which will have certain legal effects’ [translation by author]); from the general principle of good faith, therefore, follows the more specific obligation ‘de respecter les convictions que l’on fait naître par son comportement’ (‘to respect the expectations to which one’s course of conduct may give rise’ [translation by author]) (Reuter [1993] 24 and 164; cf, however, the discussion in para. 14 below as to good faith not in itself being a source of obligation where none would otherwise exist).

10  Estoppel, acquiescence, and the binding effect of unilateral declarations are different manifestations of the practical working out of the requirement of good faith, which is at the basis of all of these phenomena (Fife [2017] 26). The first, estoppel, can be divided into two categories. One is estoppel broadly conceived, which is a principle of non-contradiction (Couvreur [2017] 222). An instance of this broader version of the principle of estoppel can be found in Arbitral Award Made by the King of Spain on 23 December 1906 (1960), where Nicaragua had challenged the validity of an award, and the International Court of Justice (ICJ) held the award valid, adding that it was no longer open to Nicaragua, which, by express declaration and by conduct had recognized the award as valid, to challenge it: ‘Nicaragua, by express declaration and by conduct, recognized the Award as valid and it is no longer open to Nicaragua to go back upon that recognition and to challenge the validity of the Award’ (at 213). On the basis of this case, and the later Temple of Preah Vihear Case (1962) the International Law Commission’s Special Rapporteur on the Law of Treaties, Sir Humphrey Waldock, observed that ‘[t]he foundation of the principle [of estoppel] that a party is not permitted to benefit from its own inconsistencies is essentially good faith and fair dealing (allegans contraria non audiendus est)’ (UN ILC ‘Draft Articles on the Law of Treaties with Commentaries’ [1966] 239). Such a concept of estoppel goes far in protecting legitimate expectations. The other is the more precise principle of estoppel, which has come to prevail over time (Cottier and Müller [2021] para. 2), such that estoppel may be invoked where:

It is inherent in the nature of estoppel that it is not, in very many cases, a question of benefit to the profferor so much as damage to the profferee (Reuter [1993] 24); it is more in the nature of a shield than a sword.

11  Secondly, the ICJ has explained that acquiescence follows from the principle of good faith and ‘is equivalent to tacit recognition manifested by unilateral conduct which the other party may interpret as consent’ (Delimitation of the Maritime Boundary in the Gulf of Maine Area [1984] para. 130; Gulf of Maine Case; Tacit Agreements). There are situations where the acts of one State, such as manifestations of the display of sovereignty, ‘may call for a response if they are not to be opposable to the State in question. The absence of reaction may well amount to acquiescence’ (Sovereignty over Pedra Branca/Pulau Bati Puteh, Middle Rocks and South Ledge [Malaysia/Singapore] para. 121). This way acquiescence, too, can operate, on the basis of the interaction between States, to protect legitimate expectations (Marques Antunes [2012] 57).

12  Thirdly, international law also protects legitimate expectations by making unilateral acts binding in certain circumstances. In Nuclear Tests (Australia v France) (Nuclear Tests Cases) the ICJ observed that ‘declarations made by way of unilateral acts, concerning legal or factual situations, may have the effect of creating legal obligations’, adding that

The Court’s judgment relies on terms such as ‘trust and confidence’ (paras 46 and 51; see also Fife [2017] 26–27). International law takes a fact and context specific approach to the protection of legitimate expectations afforded by the principle of the binding nature of unilateral acts (Rodríguez Cedeño and Torres Cazorla [2019] para. 43).

13  In the investment context, the most coherent explanation of legitimate expectations is that they are the product of the broadly worded treaty obligation of the host State to accord ‘fair and equitable treatment’, underlain by its concomitant, the principle of good faith, which governs its performance. A breach by the host State of assurances, or potentially other courses of conduct, which have given rise to legitimate expectations on the part of an investor would then be contrary to good faith and on that basis violate the obligation to accord fair and equitable treatment (Tecmed v United Mexican States [2003] para. 153; Siag v Egypt [2009] para. 450; Devas v India [2016] paras 465–67; Kolb [2017] 246; Dolzer Kriebaum and Schreuer [2022] 209).

14  It is in that sense that it is correct to say, in the context of the legitimate expectations of an investor, that ‘the principle of good faith underlies fair and equitable treatment’ (Siag and Vecchi v Egypt para. 450; also El Paso v Argentina [2011] para. 348; Charanne v Spain [2016] para. 486). The Court of First Instance of the European Union has also, from the point of view of the EU legal order, pointed to the connection between the principle of good faith and the principle of protection of legitimate expectations: ‘the principle of good faith is the corollary in public international law of the principle of protection of legitimate expectations’ (Case T-231/04 Hellenic Republic v Commission para. 87; Case T-115/94 Opel Austria v Council [1997] para. 93; European Union, Court of Justice and General Court). In the interaction between good faith and the ‘fair and equitable treatment’ clause, good faith does not operate in itself as the source of obligation. That would not be in keeping with the nature of the principle of good faith, which, whilst it is ‘“one of the basic principles governing the creation and performance of legal obligations” … is not in itself a source of obligation where none would otherwise exist’ (see Border and Transborder Armed Actions [Nicaragua v Honduras] [1988] para. 94 [Border and Transborder Armed Actions Case (Nicaragua v Honduras; Nicaragua v Costa Rica)]; Land and Maritime Boundary between Cameroon and Nigeria Case [Cameroon v Nigeria] [1998] para. 39).

D.  Requirements for the Operation of the Doctrine

15  As a matter of general international law, whatever the specific doctrine relied on, there is a requirement of specificity to be met. The high bar to be met in that regard is evident from the judgment of the ICJ in Mutual Assistance in Criminal Matters (Djibouti v France) ([2008]; Case concerning Certain Questions of Mutual Assistance in Criminal Matters [Djibouti v France]). Djibouti had argued, on the basis of a letter from the Principal Private Secretary of the French Minister of Justice, that France had made an undertaking which ‘gave rise to a legitimate expectation on Djibouti’s part’ that a file concerning the death of Judge Bernard Borrel, a French national who had been seconded to the Ministry of Justice of Djibouti, would be transmitted to Djibouti (para. 126). The Court noted that the terms of the letter entailed no formal undertaking, but that the Principal Private Secretary ‘might have led his interlocutors to believe that it was simply a question of formalities and that the process would automatically result in transmission of the file’ (para. 128). That was, however, to be seen in its context, and the context was that the Principal Private Secretary was responding to Djibouti’s urgent request to expedite transmission of the file. Only investigating judges were, furthermore, competent under French law to execute letters rogatory. Against that background the Court determined that, by virtue of the content of the letter, and the factual and legal circumstances surrounding it, there was no legal obligation opposable to France to execute the international letter rogatory transmitted to it by Djibouti (Mutual Assistance in Criminal Matters [Djibouti v France] [2008] para. 130).

16  As a matter of the protection of the legitimate expectations of an investor, there are similar, if more detailed, requirements to be met. Although the underlying doctrine has been the most densely worked out in the field of investment protection, the decisions of investment tribunals are neither uniform nor consistent as regards the issue of whether protected expectations can be based only on explicit assurances, or can also arise implicitly out of courses of conduct. The question is controversial and remains to be resolved. There are, however, indications in the decisions of tribunals that it is necessary that the host State has given specific assurances to the individual investor in question (Ortiz Construcciones y Proyectos v Algeria [2020] para. 312), or to a limited class or sector of investors (National Grid v Argentina [2008] para. 177; cf, however, the discussion in Eurotunnel [Partial Award] [2007] para. 48). The relevant question tends to become whether specific commitments were made by the host State, upon which the investor could properly rely, and whether the host State adhered to such commitments (Kruck v Spain [2022] para. 161; Forteau Miron and Pellet [2022] 1495).

17  Investment tribunals have, as a general proposition, declined to sanctify laws as promises (Blusun v Italy [2016] paras 367–72). This means that provisions of general legislation ‘do not create legitimate expectations that there will be no change in the law’ (Philip Morris v Uruguay [2016] para. 426). It seems not to mean, however, that it is impossible for laws, or administrative acts, to give rise to legitimate expectations that are protected by the fair and equitable treatment standard. The standard ‘comprises an obligation to afford fundamental stability in the essential characteristics of the legal regime relied upon by the investors in making long-term investments’ (Antin v Spain [2018] para. 532).

18  There is little doubt, however, in the decisions of tribunals that legitimate expectations are an objective as opposed to a subjective concept (El Paso v Argentina para. 356). Legitimate expectations must have an objective basis and naturally cannot be fanciful or the result of misplaced optimism (Arif v Moldova [2013] para. 532). Inherent in the very concept of legitimate expectations, therefore, is a requirement for the investor to have performed adequate due diligence before making the investment (Novenergia v Spain [2018] para. 679).

19  There is also an emphasis on the element of reliance. For there to be breach, the treatment must be ‘in breach of representations made by the host State which were reasonably relied on by the claimant’ (Waste Management v United States [2004] para. 98). The reliance of an investor on the assurance of a host State is, however, not necessarily akin to acceptance of an offer, in the synallagmatic sense of contract. What is at issue is instead the more general ‘reasonable reliance interests of recipients’ (Blusun v Italy para. 372).

20  Investment tribunals have uniformly held that the investor must have held the legitimate expectations at the point in time when it made the investment (eg United Utilities v Estonia [2019] para. 606).

21  There is a question, in all of the contexts where the question of legitimate expectations arises, as to how any expectations that precede a final contractual bargain, or similar, might relate to that bargain and whether they can be characterized as legitimate expectations.

22  In the Lytton Commission of Enquiry into the Situation in Manchuria, certain declarations by China during the course of negotiations in 1905 with Japan, concerning China’s rights to construct railways in Manchuria, were held to rise to the level of commitments opposable to China (Situation in Manchuria: Report of the Lytton Commission of Enquiry [1932]). The treaty that later resulted from the negotiations contained no reference to the prohibition on Chinese construction of Manchurian railways. Nevertheless, the Lytton Commission found that the question was:

The Commission concluded that there was no doubt that the assurance was ‘a declaration or statement of intention on the part of the Chinese plenipotentiaries’ (at 44). These assurances on the part of China were in other words taken legitimately to have created expectations opposable to China.

23  It has, in the context of investment law, been observed that ‘[r]eference to a general and vague standard of legitimate expectations is no substitute for contractual rights. The relevance of legitimate expectations is not a licence to arbitral tribunals to rewrite the freely negotiated terms of investment contracts’ (Crawford [2008] 373). The same point emerges from Eurotunnel [Partial Award] [2007]. There an ‘Invitation to Promoters’, which called for tenders to develop, finance, construct, and operate a fixed link across the French Channel, had been published in the Official Journal of the European Union (para. 48). The claimants contended that the invitation had given rise to certain legitimate expectations on their part (Eurotunnel [Partial Award] [2007] para. 371) and that Clause 34.3 in the final Concession Agreement (‘no link shall be financed with the support of public funds, either directly or by the provision of government guarantees of a financial or commercial nature’) must, in order that their expectations not be frustrated, be given an extensive interpretation. The tribunal observed that there could not have been a legitimate expectation based on indications given in the Invitation because

24  On this approach, expectations born during the negotiation phase will inevitably be expunged if, in the final instrument, the policy to which the expectations were attached was not made a part of the contractual bargain. But it seems that the claimants’ argument in Eurotunnel was considered all the weaker since, first, when the negotiations were seen in the round, the alleged undertaking on which the claimants sought to base their expectations had the makings of no more than ‘a side-wind in a provision of the Concession Agreement’, that is, it could hardly be thought to be specific (Eurotunnel [Partial Award] [2007] para. 383); and, second, the initial representation was one made generally, to all potential concessionaires, in the Official Journal, and not to a more finite group of actual concessionaires.

E.  Legal Basis

25  There are, as will have been seen, certain differences between the various conceptions of legitimate expectations. On that basis, the ICJ in Obligation to Negotiate Access to the Pacific Ocean (Bolivia v Chile) (2018) refused to elide the more general protection of legitimate expectations under general international law with the protection afforded to investors under the fair and equitable treatment provisions in particular treaty instruments. Bolivia had invited the Court to hold that there was (in addition to the operation of doctrines such as acquiescence, estoppel, and the binding effect of unilateral declarations) in general international law a principle that would give rise to an obligation on the basis of what could be considered a legitimate expectation, similar or identical to the protection afforded in the investment context. The Court disagreed and observed that:

26  The fact that the Court observed that the principle in question was not in existence ‘in general international law’ would seem to mean that the principle is neither one of customary international law nor one that has the status of a general principle of law. This is so because the term general international law encompasses both of those two items (General International Law [Principles, Rules, and Standards]; Anzilotti [1929] 80–81). The idea that the protection of legitimate expectations is a general principle of law was, in other words, rejected by the Court in Obligation to Negotiate Access to the Pacific Ocean (para. 162; see also UN ILC Provisional Summary Record of the 3588th Meeting [2022] 13 [Forteau]).

27  It cannot then be correct to say that ‘[t]he protection of legitimate expectations within carefully defined limits is a general principle of law, anchored in the world’s major legal systems’ (McLachlan Shore and Weiniger [2017] 315). It also would be questionable to assume that the Court in Obligation to Negotiate Access to the Pacific Ocean rejected only that the principle was one of customary international law so that the judgment could be thought to leave open the possibility that a ‘legitimate basis for relying upon this concept is that it is a general principle of law recognized by the major legal systems of the world’ (Douglas [2023] 5; Kruck v Spain [Partial Dissenting Opinion by Zachary Douglas] [2022] para. 18).

F.  Assessment

28  There has been a tendency, in the various contexts where expectations may be protected by international law, to conceive of the legal situation along contractual lines, what has been called ‘[l]’attraction de la situation conventionnelle’ (‘the attraction of the treaty situation’ [translation by author]) (Reuter [1993] 166) (see eg Kruck v Spain [Partial Dissenting Opinion by Zachary Douglas] paras 10–13). If there is, as there must be, a distinction in kind between formalized promises of a treaty-like kind and mere assurances that give rise to expectations that are legally protected, then there needs to be a rationale that defines and explains the conditions under which expectations of that kind come into being. Just as ‘the binding nature of unilateral acts would seem to have its basis in good faith’ (UN ILC Special Rapporteur VR Cedeño ‘Fifth Report on Unilateral Acts of States’ [2002] para. 154) so, too, the basis of the protection of legitimate expectations would seem to be good faith. In the case of legitimate expectations in general international law, certain expectations, created through the course of conduct of one State, on the part of another may be protected through the operation of estoppel, acquiescence, or the binding effect of unilateral declarations, all of which are manifestations of the practical working out of the requirement of good faith. In the case of legitimate expectations in the investment context, expectations created, whether by explicit assurances or other courses of conduct, may merit protection by operation of the fair and equitable treatment standard, underlain by the requirement of good faith. In this context, ‘as in all other fields of international law, it is necessary that the law be applied reasonably’ (Barcelona Traction, Light and Power Company, Limited [1970] para. 93; Barcelona Traction Case). This will by necessity mean that there must be a limit, in the shape perhaps of a rational connection between the profferor’s assurances, or course of conduct, and the expectations, on the part of the profferee, to which international law will extend its protection.

29  The operation of good faith in this context is closely connected with legal security (Reuter [1993] 24). Although international law seeks, here as in other connections, to safeguard the value of legal security, to which both States and individuals are entitled (Ahmadou Sadio Diallo Case [Republic of Guinea v Democratic Republic of the Congo] [2010] para. 66), it does so in a manner that safeguards the fundamental principle of State sovereignty and a State’s concomitant ‘rights to exercise its sovereign authority to legislate and to adapt its legal system to changing circumstances’ (Philip Morris para. 422).

30  The extent to which the protection of legitimate expectations is a part of the ‘fair and equitable treatment’ standard at all is not free of controversy. The point has been made that the assertion that fair and equitable treatment includes an obligation not to frustrate an investor’s legitimate expectations ‘finds no express mention in investment treaties’ (Douglas [2023] 5); it ‘does not correspond, in any language, to the ordinary meaning to be given to the terms “fair and equitable”’ (Suez, Sociedad General de Aguas de Barcelona SA and Vivendi Universal SA v Argentina [Decision on Liability] [Separate Opinion of Arbitrator Pedro Nikken] [2010] para. 3). The standard of ‘fair and equitable treatment’ tends, however, to be drafted at a high level of generality. The ordinary meaning to be given to the open textured terms of the standard is entirely capable of accommodating, within defined limits, the protection of legitimate expectations. An important corollary of the fact that, in the investment context, legitimate expectations are part of a treaty standard, however, is that care must be taken in interpreting the actual text of the treaty that contains the fair and equitable treatment provision in question. Although the provisions on fair and equitable treatment in bilateral investment treaties tend to be drafted in very similar language,

it should always be remembered that each treaty is an agreement in its own right and that the words used have to be interpreted in the light of the context, object and purpose and, where appropriate, drafting history of that treaty (Greenwood [2015] 53).

Whether the question of legitimate expectations arises under general international law or under a particular treaty, however, the common thread is that governing the creation, interpretation, and performance of the obligations in question will be the principle of good faith.