Pocket Notes

Law Beyond Borders – International Law

Credits – Dmytro Novitskyi

International law, also known as public international law and the law of nations. It is the set of rules, norms, and standards generally accepted in relations between nations. It establishes normative guidelines and a common conceptual framework to guide states across a broad range of domains, including war, diplomacy, trade, and human rights. 

International law thus provides a means for states to practice more stable, consistent, and organized international relations. Example – International Law in Human Rights. 


According to Black’s Law Dictionary ‘the legal system governing the relationship between nations; more modernly and the Law of International Relations, not only nations but also such participants as International organization and individuals.

The definition states that not only law set by International Organizations like the United Nations amount to international law but also the rules set by signing the treaties also amount to the same.

Sources of International Law

Sources of international law refer to where states, organizations, individuals, and courts can find principles of international law.  One broadly accepted definition of sources of international law includes Article 38 of the ICJ Treaty.  According to this article, the International Court of Justice shall apply the following sources of law, ranked in order of precedence: 

  • International conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
  • International custom, as evidence of a general practice accepted as law;
  • The general principles of law recognized by civilized nations;
  • Subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law


The ICJ’s statute refers to ‘International Custom, as evidence of a general practice accepted as law,‘ as a second source of international law.

Custom, whose importance reflects the decentralized nature of the international system, involves two fundamental elements: the actual practice of states and the acceptance by states of that practice as law. The actual practice of states (termed the material fact) covers various elements, including the duration, consistency, repetition, and generality of a particular kind of behavior by states. All such elements are relevant in determining whether a practice may form the basis of a binding international custom.

The ICJ has required that practices amount to a ‘constant and uniform usage‘ or be ‘extensive and virtually uniform‘ to be considered binding. Although all states may contribute to the development of a new or modified custom, they are not all equal in the process. The major states generally possess a greater significance in the establishment of customs.

For example, during the 1960s the United States and the Soviet Union played a far more crucial role in the development of customs relating to space law than did the states that had little or no practice in this area. After a practice has been established, a second element converts a mere usage into a binding custom—the practice must be accepted as opinio juris sive necessitatis (Latin: ‘opinion that an act is necessary by rule of law‘). In the North Sea Continental Shelf cases, the ICJ stated that the practice in question must have ‘occurred in such a way as to show a general recognition that a rule of law or legal obligation is involved.

Once a practice becomes a custom, all states in the international community are bound by it whether or not individual states have expressly consented—except in cases where a state has objected from the start of the custom, a stringent test to demonstrate. A particular practice may be restricted to a specified group of states (e.g., the Latin American states) or even to two states, in which cases the standard for acceptance as a custom is generally high. Customs can develop from a generalizable treaty provision, and a binding customary rule and a multilateral treaty provision on the same subject matter (e.g., the right to self-defense) may exist at the same time.

General principles of law

Yet another source of international law identified by the ICJ’s statute is ‘the general principles of law recognized by civilized nations.’ These principles essentially provide a mechanism to address international issues not already subject either to treaty provisions or to binding customary rules. Such general principles may arise either through municipal law or through international law, and many are in fact procedural or evidential principles or those that deal with the machinery of the judicial process—e.g., the principle, established in Chorzow Factory (1927–28), that the breach of an engagement involves an obligation to make reparation. Accordingly, in the Chorzow Factory case, Poland was obliged to pay compensation to Germany for the illegal expropriation of a factory.

Perhaps the most important principle of international law is that of good faith. It governs the creation and performance of legal obligations and is the foundation of treaty law. Another important general principle is that of equity, which permits international law to have a degree of flexibility in its application and enforcement. The Law of the Sea treaty, for example, called for the delimitation on the basis of equity of exclusive economic zones and continental shelves between states with opposing or adjacent coasts.

Other sources

Article 38 (1) of the ICJ’s statute also recognizes judicial decisions and scholarly writings as subsidiary means for the determination of the law. Both municipal and international judicial decisions can serve to establish new principles and rules. In municipal cases, international legal rules can become clear through their consistent application by the courts of a number of states. A clearer method of law determination, however, is constituted by the international judicial decisions of bodies such as the ICJ at The Hague, the UN International Tribunal for the Law of the Sea at Hamburg (Germany), and international arbitral tribunals.

International law can arise indirectly through other mechanisms. UN General Assembly resolutions, for example, are not binding—except with respect to certain organizational procedures—but they can be extremely influential. Resolutions may assist in the creation of new customary rules, both in terms of state practice and in the process of establishing a custom by demonstrating the acceptance by states of the practice as law (the opinio juris).

For this to occur, a resolution must contain generalizable provisions and attract substantial support from countries with diverse ideological, cultural, and political perspectives. Examples of such resolutions include the Declaration on the Granting of Independence to Colonial Countries and Peoples (1960), the Declaration on the Legal Principles Governing Activities of States in the Exploration and Use of Outer Space (1963), and the Declaration on Principles of International Law Concerning Friendly Relations and Co-operation Among States (1970).


The Vienna Convention on the Law of Treaties of 1969 (VCLT) is the main instrument that regulates treaties. It defines a treaty and relates to how treaties are made, amended, interpreted, how they operate and are terminated. It does not aim to create specific substantive rights or obligations for parties – this is left to the specific treaty (i.e. the Vienna Convention on Diplomatic Relations creates rights and obligations for States in their diplomatic relations).

VCLT is a ‘treaty on treaties.

Definition of Treaty

Article 2(1) (a) of the VCLT talks of ‘treaty‘. It means an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation.