Estoppel in Public International Law

In our research on Space Law, let’s focus for this new article on Space Legal Issues on Public International Law and Estoppel in Public International Law. The term estoppel, from the French estouppail, is defined by the Oxford English Dictionary as “The principle which precludes a person from asserting something contrary to what is implied by a previous action or statement of that person or by a previous pertinent judicial determination”.

In Public International Law, the doctrine of estoppel protects legitimate expectations of States induced by the conduct of another State. The term stems from common and Anglo-American law, without being identical with the different forms found in domestic law. It is supported by the protection of good faith (bona fide) in the traditions of civil law. Despite varying perceptions and definitions in doctrine and practice, the features and essential components of estoppel in public international law are generally accepted today.

As it is most commonly described, “estoppel is a rule of international law that bars a party from going back on its previous representations when those representations have induced reliance or some detriment on the part of others”. Although estoppel is now a firmly established rule of international law and is being invoked and applied in an increasingly wide variety of contexts, international lawyers have yet to uncover all its secrets.

Public International Law

Public international law refers to all the legal rules governing international relations between public entities such as States and international organisations. In order to settle an international public law dispute, it is the International Court of Justice (ICJ) sitting in The Hague (Netherlands) that may be seized. The International Court of Justice is the principal judicial organ of the United Nations.

According to Velimir Zivkovic, “public international law is, most broadly speaking, a system of norms that governs relationship between legal entities recognized in the sphere of international law; primarily although not exclusively sovereign states an international organizations. It is further fragmented into a number of branches, but it is generally considered to have overarching common principles. Private international law has a bit of deceiving name. It is actually a branch of national laws that deals, mostly, with determining what the applicable law should be when there is a foreign element in the relationship (foreign national involved, place of event was abroad, etc.). It is actually called in common law states conflict of laws which perhaps explains it better”.

The principle of good faith, both a general principle of law and a general principle of international law, plays an eminent role in international treaty relations in general and in international economic relations in particular. Its manifold expressions and concretisations, such as pacta sunt servanda, estoppel, acquiescence, equity and abuse of rights, remain highly significant in international adjudication. However, to determine the exact content of good faith and its manifestations can be a daunting task.

Estoppel in Public International Law

International law has long recognised the doctrine of estoppel, a principle which prevents states from acting inconsistently to the detriment of others. Until the 1980s, the use of estoppel in Public International Law was limited to cases involving territorial claims. International estoppel is based on good faith and promotes consistency in international relations. It is a broad concept, capable of myriad applications, and as a “general principle of law recognized by civilized nations”, it carries persuasive moral weight that can be applied in the International Court of Justice (ICJ).

The historical roots of estoppel in the common law tradition make it worthwhile (though probably not absolutely necessary) to explore the variety and development of estoppel in that tradition and the possible counterparts of estoppel in other national legal systems. Estoppel is almost always discussed in relation to other, neighbouring concepts and principles of international law, so it is essential to take into account not only broad treatments of “general principles” in international law, but also works on acquiescence, preclusion, prescription, waiver, unilateral acts and declarations, the protection of reasonable/legitimate expectations, good faith, equity, and so on. Many useful discussions and analyses of estoppel are context-specific, so research on estoppel should also take in some aspects of specialist literature on acquisition of territory, international adjudication, protection of foreign investment…

The international rule of estoppel has a historic basis both in Anglo-American Common Law (known as judicial precedent or judge-made law, or case law) and in the European civil law systems, which have an analogous concept of “preclusion” or “foreclusion”. Nonetheless, international estoppel differs from its Common and Civil Law ancestors. While good faith forms the conceptual basis for international estoppel, the promotion of consistency provides its practical purpose.

International estoppel requires satisfaction of three elements. First, the statement creating the estoppel must be clear and unambiguous; second, the statement must be voluntary, unconditional, and authorised; and finally, there must be good faith reliance upon the representation of one party by the other party either to the detriment of the relying party or to the advantage of the party making the representation. The first two elements have sparked little controversy; the third, however, has occasioned much debate.

Claims of international estoppel arise in two contexts: unilateral declarations and acquiescence. Though facially dissimilar in some regards, the requirements and applications of estoppel are essentially the same in both contexts. A state may act unilaterally in one of two ways: it may make a unilateral promise or it may make a unilateral statement of fact. Either may give rise to an estoppel.

Estoppel may also arise out of a state’s acquiescence to the declaration of another state or to existing circumstances: “The few writers who have discussed the question have had no doubt that acquiescence was apt to found an estoppel provided that the circumstances were such that acquiescence could be equated with recognition or consent”. If the requirements of estoppel are met, the silence binds the acquiescing state.

The World Court has bound a state by its previous actions on many occasions. Some involved unilateral declarations, while others involved acquiescence. In none of these cases did the Court identify the doctrine that justified its holding. However, all four contained references to good faith, consistency, or intent to be bound, language that supports an estoppel theory.

Concluding remarks

The means by which estoppel became such a “well-established principle” of international law are not so easily identified. According to Ian Brownlie, a British practising barrister, specialising in international law, there are four elements which must be satisfied for a practice or custom to become law under Article 38(1)(b): 1) duration, 2) consistency of practice, 3) generality of practice, and 4) opinio juris sive necessitatis.

As a conclusion, speaking about Estoppel in Public International Law, contemporary practice shows that arguments about estoppel are as likely to appear in the context of a dispute about international trade or human rights as they are to appear in the context of (more traditional) disputes about title over territory or nationality. But important disagreements and unresolved questions still remain about the practical requirements of estoppel (and, in particular, the need for detrimental reliance); its relationship to neighbouring concepts, such as acquiescence; its proper categorisation among the sources of international law; the significance of common law estoppel and its counterparts in other legal systems for the purposes of international law; and the normative basis of estoppel, especially its relationship with broader principles of international law, such as good faith and equity. That is what we can say about Estoppel in Public International Law.