Sources of International Law

Author: Harshika Gupta


International law encompasses a set of regulations and guidelines that dictate how state and non-state entities should interact, as determined and explained by various legal experts. Its roots can be traced back to a distinct foundation and did not emerge from thin air. Drafting international law is a meticulous and intricate process that entails thoughtful deliberation. The term “source” is an ambiguous one and may refer to legal principles, historical events, ethical considerations, or any other basis for law.

When referring to the sources of law, what is truly meant are the processes or procedures used to develop, decide upon, or identify international legal norms? There are many sources of law, and they are divided into formal and material sources based on their nature. Salmond summarizes formal sources of law as where the law gets its power and legitimacy, and material sources as from where matter is derived. The origins of international law are not as obvious as those of national legal systems, however Article 38 of the statute of the International Court of Justice is broken into two paragraphs, the first of which indicates that the court may turn to the following while determining on any international dispute-


Treaties and international conventions,

General principles of law recognized by the civilized nation,

Judicial decision,

Juristic work of the highly qualified individuals,

General assembly resolutions and declarations.

Article 38, paragraph 2, authorizes the court to determine a matter ex aequoet bono, which means that adjudicators should resolve disputes in a “fair” and “good conscience” manner provided the parties agree. This is not an exhaustive list, but it serves as a good starting point.


Custom, in its legal sense, goes beyond mere habit or routine. It refers to a practice that individuals feel obligated to follow, believing that failure to do so would result in a loss or sanctions. International law has its roots in custom, which has developed over time through practical implementation by states. Customary international law is the result of a state’s ongoing and consistent practice, coupled with a sense of legal duty or responsibility towards it. In various cases it has been accepted that there are two elements of a custom, one being subjective and other objective –

General Practice: It is confirmed through the general practice of a state and its repetition without interruption by states.

Legal nature of practice (Opinio juris): It is the psychological element, and refers to the feeling on states part towards the fulfillment of its legal obligation.

The process of Opinio juris does not require a long period, it can be recognized instantly, the same was clarified by ICJ in North Sea Continental Shelf Germany v. Denmark. It was observed that customary law can evolve instantaneously, and opinio juris can form quickly.

To put it briefly, customary international law is based on the consistent behavior of the majority of the international community. Examples of customary international law include the prohibition of arbitrary deprivation of life, torture, and direct attacks on people and civilian objects during armed conflicts. However, the significance of custom has decreased over time due to the gradual codification of laws and the creation of various law-making treaties. Nevertheless, the evolution of custom is a dynamic process that plays a crucial role in filling in legal gaps and resolving uncertainties and omissions caused by other sources.


Agreements between States, also known as treaties, conventions, or exchanges of notes and protocols, are a significant source of law. Such agreements create legal obligations for the signatories and can take the form of conventions or protocols as mentioned earlier. Treaties are commonly created to keep up with the changing needs of the dynamic international society. According to international law, states can establish laws through mutual agreement,

so treaties serve as a means of regulating state behavior and creating laws. However, it’s important to note that treaties are not a source of law, but rather a source of obligation under the law. Only states that become parties to a treaty are legally bound by it, and it’s ultimately up to each state to decide whether or not to participate in a treaty – there are no requirements to do so.

Treaties are the closest thing to state law since they are a legal instrument binding all of its signatories to execute all of the obligations agreed upon during such agreement. We may compare treaties to private contracts between parties to an agreement that create rights and duties. Treaties with a contractual nature are debatable as a source of international law because their primary purpose is to create obligation and have no control over non-signatory parties and do not ipso facto bind them, whereas treaties with a constructive and dispositive nature, i.e. treaties setting international boundaries and creating obligations for third parties, such as the Treaty of Vienna of 25 March 1815, are exception to this.

There are two types of treaties: law-making treaties and treaty contracts. Law-making treaties have universal application and create general norms for future conduct of contracting parties. On the other hand, treaty contracts are only relevant to the contracting states.

Finally, the question arises: as the contractual terms are binding in municipal law because the contract act provides for it. Then what about the obligation of a treaty? What gives it a binding effect? The answer is that treaties are legally binding due to a customary rule of international law that deems them so, i.e. there exists a customary rule of international law that treaties are binding, getting along with the legal maxim pacta sunt servanda which means treaties must be adhered.


The demand for appropriate international law is increasing as modern world civilization develops. The same cannot be overcome just by custom and treaties; advanced and complex legislation, similar to municipal law in many states, is necessary. Due to the inadequacy of international law, a judicial tribunal adjudicating an international issue may encounter a scenario that cannot be addressed by the currently established norms of international law.

To avoid such a predicament, the international arbitration tribunal previously referred to general principles of law of civilized states as a source. However, as time passed, the distinction between civilized and non-civilized states became blurred, and now “all nations are considered civilized.” Having a nation’s general principles of law as a basis of international law implies that international courts can rely on legal standards that are well-established in the local legal systems of diverse states. However, this isn’t the sole interpretation; it also refers to legal ideas developed from current international practice.

The concept discussed here primarily pertains to evidence, processes, and principles that have been widely accepted by many governments worldwide. One example is the recognition of the legal personality of companies, as seen in the Barcelona Traction Co. case (1970), which is generally acknowledged in national legal systems. In the Corfu Channel case, the court allowed circumstantial evidence on the basis that indirect evidence is accepted in all systems and by international agreements.


According to article 38(1)(d), court judgements are a secondary means of determining international law. Only the parties involved are bound by these judgements, as stated in Art. 59 of the ICJ Statute. This means that the ICJ is not obligated to follow its own previous decisions and the principle of stare decisis does not apply. However, the ICJ and other international tribunal often refer to past cases when dealing with matters of international law. Therefore, it would be incorrect to consider these references as unimportant or “subsidiary.”

Similarly, significant judgments of municipal courts are considered in settling any issue but are not binding on the ICJ. The persuasiveness of a court judgement is enhanced if it is independent, unbiased, and erudite. Another variable considered is a unanimous verdict with no dissenting standpoint.


The works and teachings of skilled jurists and publicists have greatly aided the advancement of international law. Although they are not legally binding, these secondary sources offer valuable perspectives on a range of topics. Through their extensive research and expertise, these individuals have played a key role in shaping the current state of international law. Notable figures such as Oppenheim in public international law and Gidel in the law of the sea have made significant contributions, as have many others in the field.


Critics often point out that Article 38 of the Statute fails to include the Acts of United Nations organs, which are considered highly significant in the development of international law. It is possible that such actions may actually fall within the scope of Article 38 more than commonly believed, while some may argue that the list in Article 38 is complete, this viewpoint can also be disputed. As the task of codifying international law is currently underway and resides with the International Law Commission, the UN General Assembly can provide advisory opinions through resolution in accordance with Article 13 of the UN Charter, which gives the UNGA the authority to initiate studies and make recommendations for this purpose, but the same is not binding on the commission because the UN Charter is silent on the subject. In today’s constantly evolving world, it’s crucial for international law to keep up with the times. To ensure that nothing falls through the cracks, various sources are used to help codify this law. The scope of this legislation is wider than anything that’s been seen before, and it applies equally to every state.