Sources of International Law

International law plays a vital role in adjudicating points of conflict between two or more nations. It is traced back to the period of the European Renaissance. It is one such law that has evolved through the years considering all kinds of changes internationally and their impacts. This article helps to understand the basics of International Law. It gives a brief account of the types of International Law. The article then speaks about the sources of International law. It covers various elements like Treaties, Customs, and General Principles and so on as the sources of International law. It works its way to the conclusion pondering upon how International law is implemented in India.


What is International Law?

Every state (nation) has their own respective domestic laws which regulate the conduct of its citizens. These laws also conduct and regulate the affairs of the state machinery (government). 

But what happens when there is a dispute between two state parties or between two nations? Who governs such disputes? And who regulates the conduct between two or more nations? 

The answer lies in International Law.

Many scholars trace the roots of International Law back to the periods of European Renaissance or different civilizations such as the Roman Empire or the ancient Middle East.

The International law as known to us today took its form during the expansionist and industrial era. It became truly ‘international’ post World War II owing to the rapid decolonization that took place. At the same time, international organisations like the United Nations [1] with its organs came into existence.   

International Law hence can be understood as a framework of rules and principles binding the relations between states and their conduct among themselves.

It relies on consent-based governance to a great extent, though certain aspects are exceptions to the consent requirement. 

Types of International Law

International law can be categorized into:

  1. Public International law– It deals with interstate regulations, fostering stable and organized international relations. In simpler terms, it deals with regulating the conduct of one state with another. It is applicable to Finance, Sea, Intellectual Property, Trade, Weapons, Climate change, etc.
  2. Private International Law– It is a set of rules and regulations that governs the dispute, interaction and transactions between private parties of two or more different states (nations). Various international bodies work on harmonizing private international law. Such as ICSID [2], UNDROIT [3], UNCITRAL[4] and so on.

Sources of International Law

As far as the sources of Domestic law are concerned, it is quite easy to pinpoint. In case any lacking is found in such laws, it can be rectified by domestic courts.

But, in the case of International law, the sources are not condensed; rather they are a wide array of resources, put together.

The most authoritative source of international law is Article 38(1) of the Statute of the International Court of Justice. It provides the outline which applies when a court is to deal with disputes relating to international law. It says:

“1. The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:

  1. international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;

  2. international custom, as evidence of a general practice accepted as law;

  3. the general principles of law recognized by civilized nations;

  4. 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.

2. This provision shall not prejudice the power of the Court to decide a case ex aequo et bono if the parties agree thereto.” [6]

Though the said statute is applicable to the International Court of Justice (ICJ). The function of the court is to decide disputes submitted to it, concerning international law and all UN members are Ipso facto (Latin: By the fact itself) members of ICJ, hence, it is widely accepted.


A treaty/ International Convention/ Charter refers to a legally binding, written agreement in which states agree to act in a particular manner as prescribed by the agreement. 

They are often regarded as complex documents especially those which involve more than two states (nations).

Treaties are often entered in good faith between two states and are legally binding.

Such Agreements between nations that do not have any binding obligations cannot be referred to as treaties. Though such agreements are prone to having political effects alone.

A treaty may not be a single document but a series of related documents also constitutes a treaty.

They may be drafted between states by their leader or representatives of government departments depending on the circumstances.

There are a number of steps/ procedures undertaken to convert a draft into a binding treaty.

The final draft has to be “adopted” in an international conference by the way of a two-thirds majority.

Ways of expressing consent to a treaty by states:

  1. Consent by signature:

In some cases, treaties are brought into effect by the way of signatures of the representatives.

These representatives are given authorization in writing from their respective state to act on behalf of it.

  • Consent by the exchange of instruments:

In some cases, consent is expressed by the way of exchange of certain instruments. Such an instrument may be a document containing terms and conditions agreed by both and all the parties to the treaty.

  • Consent by ratification:

Ratification is simply the act of the State by doing which the state expresses its consent to be bound by the regulations of a treaty. Ratification differs from state to state but usually requires a sign or act expressing the willingness of the states to be a part of a treaty. 

Such an act could be an assent by the President of the State or require a vote of a majority in the legislature. 

In multilateral treaties, involving a number of countries, ratification is usually the most preferred method of expressing assent where one party collects the ratification of the others.


ICJ Statute in its Article 38(1) refers to “international custom, as evidence of a general practice accepted as law,”. 

„(…) not only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it (…) The States concerned must therefore feel that they are conforming to what amounts to a legal obligation.” North Sea Continental Shelf case – ICJ, 1969 [7]

The elements of customary international law include:

1. Popular repetition by States of similar international acts over time (State practice).

2. Acts must occur out of a sense of obligation (opinio juris). 

3. Acts must be taken by a notable number of States and not be rejected by a significant number of States.

 Further, customs broadly involve two basic elements: the actual practice of the custom in the states and the acceptance by states of that practice as law. 

The actual practice of states covers various elements, like the duration of the custom or the time period over which the custom took place or was into practice, consistency, repetition, and generality of a particular kind of behaviour by states. All these elements are taken into consideration to determine the obligatory or binding nature of a custom in international law. 

The ICJ has clarified that practices amounting to a “constant and uniform usage” or be “extensive and virtually uniform” to be considered binding. Although a lot of states are involved in carrying a practice forward, the majority of them are responsible for the establishment only.

After a practice has been established, a second element requires the practice to be accepted as opinio juris sive necessitatis (Latin: “opinion that an act is necessary by rule of law”). 

Once a practice becomes a custom, all states in the international community are bound by it except for the cases where a state has shown strict opposition to such practice or the custom in question is contradictory to the laws and policies of that state. 

A particular practice may also be restricted to a specified group of states. Customs develop from a generalizable treaty provision to a binding customary rule to a multilateral treaty provision on the same subject matter.

However, in some cases, it is still unclear so as to how one can identify a rule of international custom or how one can prove its existence. [8]

General principles of International law

The third source of international law identified by the ICJ’s statute is “the general principles of law recognized by civilized nations.” 

Such general principles majorly arise either through municipal law or through international law.

Perhaps it can be said that the most important principle of international law is that of good faith. It governs the creation and performance of legal obligations and is the sole foundation of treaty law.

Another important general principle is that of equity, which permits international law to have a range of flexibility in its reinforcement and implementation. 

General principles are interconnected to treaty law and custom.

ICJ decisions

Article 38 (1) of the statute of the International Court of Justice, also recognizes judicial decisions and scholarly writings as subsidiary means for the establishment of the law. Both municipal and international judicial decisions can serve as sources of international law. A more effective method of law determination constitutes 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 and so on. 

Article 59 of the statute of the ICJ states that the decision of the ICJ does not have a binding force except on the parties involved in the dispute. However, ICJ does work on judicial precedent [5]

Furthermore, International law can arise indirectly through other mechanisms as well. For example, the UN General Assembly resolutions are not binding (except with respect to certain organizational procedures) but they can prove to be highly influential. Resolutions may assist in the creation of new customary rules and impact the formation of various laws and policies in the future.

For this to happen, a resolution so passed 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).

Unilateral actions by a state may give rise to legal obligations when it has been made clear that the state intends to be bound by the obligation and also when its intention is publicly announced.

International law and India

Article 51 of the Constitution of India states that “The State shall promote international peace and security by the prescription of open, just and honourable relations between nations, by the firm establishment of the understandings of international law as the actual rule of conduct among governments and by the maintenance of justice and respect for treaty obligations in the dealings of organised people with one another.”

Under Article 253 of the Constitution of India, the Parliament and the Union of India are at the liberty to implement treaties and can even interfere in the powers of the state government to ensure implementation of an international treaty.

In the landmark case of Kesavananda Bharati v. the State of Kerala,[10] it was observed that the courts must interpret the provisions of the Indian constitution in the light of the Charter of the United Nations.

In the case of Magan Bhai Patel v. Union of India [11], it was held that if a treaty or agreement restricts or modifies the rights of the citizens or the laws of the state, the respective treaty or agreement would be enforced by a legislative measure.

If there is no restriction or modification of laws or rights there shall be no need for any legislative act.

It is very clear that any international law cannot, by nature, override domestic law of the land in India. So to enforce any such law it is adopted by the legislature as a part of the domestic law.

However, in the case of Sheela Barse v. Secretary Children’s Aid Society [12], the Hon’ble Supreme Court held that India ratified conventions regarding the protection of children and the state government has an obligation to implement those principles.

The most revolutionary use of international law in India has been in the case of Vishaka v. The State of Rajasthan [13], where the court used provisions of the Convention on Elimination of all Forms of Discrimination against Women, (CEDAW), to create legally binding provisions regarding sexual harassment. [9]


From the above article, one can conclude what is International law, how it came into existence and what are its types. We also learn about the various sources of law. The ICJ statute being the primary source of International Law. Further International rules are enforced by the way of treaties and then the recognition of generalized customs. 

International obligations come into place as a result of general principles known i.e. agreement on the basis of good faith and the principle of equity. And finally, the ways by which ICJ decisions are influential on International law, that is, by the way of Judicial Precedent.

As far as an implication of International law in India is concerned, it can be seen that it is done by the way of ratification, i.e. adopting the International principles in domestic law by the act of parliament or interpretation by the courts.

One must also bear in mind, in addition to the above-mentioned points, that the sources that are of recent origin are generally seen as more authoritative, and specific rules take precedence over general rules. 

Jus cogens (Latin: “compelling law”) rules are peremptory norms that cannot be ignored by states; they hold a higher binding status than jus dispositivum (Latin: “law subject to the dispensation of the parties”), or normal international rules, prone to the relaxation of choice of the states to be adopted. 

The former category includes the prohibitions against genocide, slavery, and piracy and the outlawing of aggression and so on. 

International law has established a category of erga omnes (Latin: “toward all”) obligations, which apply to all states. The breach of such obligation may lead to action from all the states as they hold the interest of all the states.


What is international law?

International Law can be understood as a framework of rules and principles binding the relations between states and their conduct among themselves.

What are treaties?

A treaty/ International Convention/ Charter refers to legally binding, written agreement in which states (two or more) agree to act in a particular manner as prescribed by the agreement. 

Treaties are often entered in good faith between two states and are legally binding.

What is ICJ?

ICJ or International Court of Justice is one of the six principal organs of the United Nations. It settles disputes between states with respect to International law.

How can custom be a source of International law?

For a custom to be recognised as a source of law it must include the following elements:

  1. Popular repetition by States of similar international acts over time (State practice).
  2. Acts must occur out of a sense of obligation (opinio juris). 
  3. Acts must be taken by a notable number of States and not be rejected by a significant number of States.

How does India express its consent towards International treaties?

It is often observed that India expresses its consent to International law and principles by the way of Ratification. In simpler terms, by adopting the respective principles in the domestic law by an act of the legislature or through courts.


  10. Kesvananda Bharati v. The State of Kerela writ petition (Civil) 135 0f 1970

  1. Magan Bhai Patel v. Union of India 1969 AIR 783

  1. Sheela Barse v. Secretary Children’s Aid Society 1987 AIR 656

  1.  Vishaka & Ors v. The State of Rajasthan AIR 1997 SC 3011

Book referred: Legal Studies for Class XII (CBSE) Approved by Bar Council of India

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