Sources of International Law

Introduction

The sources of International Law are the foundations from which the rules and principles governing relations between states and other international actors emerge. Understanding these sources is essential for determining what constitutes binding international obligations. Since there is no central legislative authority in the international legal system, laws are derived from state practice, agreements, customs, judicial decisions, and scholarly writings.

The Statute of the International Court of Justice (ICJ), under Article 38(1), provides the most authoritative list of sources of international law. It identifies both primary and subsidiary sources.

---

Article 38(1) of the ICJ Statute

Article 38(1) of the Statute of the International Court of Justice (1945) provides:

“The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:
(a) International conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
(b) International custom, as evidence of a general practice accepted as law;
(c) The general principles of law recognized by civilized nations;
(d) 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.”

Thus, the primary sources of International Law are:

1. International Conventions or Treaties
2. International Customary Law
3. General Principles of Law Recognized by Civilized Nations

and the subsidiary sources are:
4. Judicial Decisions
5. Teachings of Jurists and Publicists

---

1. International Conventions and Treaties

Meaning and Importance

Treaties are written agreements between two or more states or international organizations that create legal obligations. They are the most formal and deliberate source of international law and may be bilateral, multilateral, or universal.

Types of Treaties

• Law-making treaties: Establish general rules of international law (e.g., UN Charter 1945, Geneva Conventions 1949).
• Treaty contracts: Create specific obligations between parties (e.g., trade or boundary agreements).

Formation and Validity

The process of treaty formation is governed by the Vienna Convention on the Law of Treaties, 1969, which defines terms like:

• Ratification: Formal confirmation by a state to be bound by a treaty.
• Accession: When a state joins an already existing treaty.
• Reservation: A statement made by a state excluding or modifying certain provisions of a treaty.

Case Laws:

1. North Sea Continental Shelf Cases (1969) – ICJ Link
   • The ICJ emphasized that treaties can codify or crystallize existing customary laws.
2. Aegean Sea Continental Shelf Case (1978) – ICJ Link
   • The Court held that consent of states is vital for a treaty’s binding nature.

---

2. International Customary Law

Meaning

Customary International Law arises from the consistent and general practice of states followed out of a sense of legal obligation (opinio juris). It is considered binding on all states except those that have persistently objected to it.

Essential Elements

1. State Practice: Actual and consistent behavior of states.
2. Opinio Juris: The belief that such practice is legally obligatory.

Formation of Customary Law

Customary rules evolve gradually through consistent repetition of similar acts and acceptance by states.

Case Laws:

1. Asylum Case (Colombia v. Peru, 1950) – ICJ Link
   • The ICJ held that local or regional customs must be proven by consistent and accepted practice among states concerned.
2. North Sea Continental Shelf Cases (1969) –
   • The Court explained that for a practice to become customary law, it must be “extensive and virtually uniform.”
3. Nicaragua v. United States (1986) – ICJ Link
   • The ICJ reaffirmed that customary law exists independently of treaty law and both can coexist.

---

3. General Principles of Law Recognized by Civilized Nations

Meaning

These principles are derived from the common legal systems of the world and are used to fill gaps when no treaty or custom applies. They ensure that international law remains a complete legal system.

Examples:

• Principle of good faith
• Doctrine of res judicata (finality of judgments)
• Principle of equity
• Doctrine of estoppel

Case Laws:

1. Chorzów Factory Case (1928) – ICJ Link
   • The PCIJ held that reparations must “wipe out all the consequences of the illegal act,” applying the general principle of restitution.
2. Barcelona Traction Case (1970) – ICJ Link
   • The ICJ referred to good faith and abuse of rights as general principles of international law.

---

4. Judicial Decisions

Role and Relevance

While judicial decisions are subsidiary sources, they are influential in clarifying and interpreting international law. The ICJ’s judgments do not bind non-parties (Article 59 of the Statute), but they are persuasive precedents.

Examples:

• Decisions of the International Court of Justice (ICJ)
• International Criminal Court (ICC)
• European Court of Human Rights (ECHR)
• WTO Dispute Settlement Body

Judicial decisions contribute to the progressive development of international law and promote consistency and predictability.

Case Laws:

1. Corfu Channel Case (1949) – ICJ Link
   • The Court emphasized state responsibility for failing to prevent harm to foreign states.
2. Nicaragua v. United States (1986) –
   • The ICJ’s reasoning became a precedent for defining “use of force” under customary law.

---

5. Teachings of the Most Highly Qualified Publicists

Meaning and Importance

The writings and teachings of recognized scholars and jurists help identify and interpret international legal principles. Although they are not binding, they serve as subsidiary means for determining rules of law under Article 38(1)(d).

Notable Jurists:

• Hugo Grotius – De Jure Belli ac Pacis (1625)
• Oppenheim – International Law: A Treatise
• Ian Brownlie – Principles of Public International Law
• Malcolm N. Shaw – International Law

These scholars’ analyses are often cited by international courts and tribunals for authoritative interpretation.

---

Additional Sources (Emerging Sources)

1. Resolutions of International Organizations:
   • Although not binding, UN General Assembly resolutions (like Declaration on Friendly Relations, 1970) influence customary law formation.
2. Soft Law Instruments:
   • Declarations, codes of conduct, and guidelines, e.g., Universal Declaration of Human Rights (1948), often lay the groundwork for binding treaties.
3. Decisions of International Conferences:
   • Declarations from global conferences (e.g., Rio Declaration on Environment and Development, 1992) also shape evolving norms.

---

Conclusion

The sources of international law reflect its decentralized and evolving nature. Treaties codify clear obligations, customs embody consistent state practice, and general principles ensure justice and completeness. Judicial decisions and scholarly writings further refine and clarify these norms. Together, they ensure that international law remains dynamic, adaptable, and effective in regulating the conduct of states and international actors.

Also Read: Essentials of a Valid Contract

National Moot Court Competition 2025 Hybrid Legal Advocacy Opportunity at Amity University Rajasthan, Jaipur; Apply by October 26, 2025