Sources of International Law: Treaty, Custom and General Principles Explained

In an era of increasing global interdependence, international law forms the invisible yet powerful thread that weaves nations into a cooperative legal order. From climate change negotiations to maritime boundaries, from refugee protection to cyber governance — international law governs the conduct of states, international organizations, and, at times, individuals. But where does this law draw its authority from?

Article 38(1) of the Statute of the International Court of Justice (ICJ) stands as the cornerstone in this regard. It identifies three principal sources: treaties, customary international law, and general principles of law recognized by civilized nations. Each source plays a distinct role in shaping international obligations, and India’s legal engagement with these sources offers significant insights for both lawmakers and

the judiciary.

Treaties: The Charter of Consent

Treaties are the most visible and formal source of international law. These are agreements, either bilateral or multilateral, which become legally binding once signed and ratified by states. Often likened to contracts between countries, treaties lay down rights and obligations on diverse subjects ranging from trade to terrorism, and from environmental protection to human rights.

India’s approach to treaties is governed by a dualist system — treaties are not automatically enforceable unless implemented through domestic legislation. Yet, their persuasive value in judicial interpretation is undeniable. Take the landmark case of Vishaka v. State of Rajasthan (1997), where the Supreme Court relied on the Convention on the Elimination of All Forms of Discrimination Against Women (CEDAW) to frame guidelines against sexual harassment at the workplace. Even though CEDAW had not been enacted into Indian law, its principles guided the Court to uphold the dignity of working women.

Similarly, India’s ratification of the Paris Agreement has impacted domestic environmental jurisprudence, with courts increasingly referring to international commitments when interpreting the “right to life” under Article 21 of the Constitution.

Customary International Law: The Law of Habit and Belief

Unlike treaties, customary international law arises from consistent state practice accompanied by opinio juris — the belief that such practice is legally required. Though unwritten, customs enjoy universal acceptance and binding force, even for non-signatory states.

India has demonstrated respect for numerous customary norms. A significant example is its adherence to the principle of non-refoulement, which prohibits sending refugees back to a place where they may face persecution. Although India is not a party to the 1951 Refugee Convention, Indian courts, particularly in the cases decided by the Delhi and Madras High Courts, have upheld this principle while dealing with asylum-seekers from Myanmar and Sri Lanka.

Another relevant custom is the freedom of navigation under international waters. India follows this norm in accordance with UNCLOS, promoting maritime peace and stability — especially in the strategically significant Indian Ocean region.

General Principles: The Universal Language of Justice

The third primary source, as per Article 38(1)(c), is the general principles of law recognized by civilized nations. These principles, such as equity, good faith, and natural justice, bridge the gap when neither treaty nor custom applies.

Indian constitutional and administrative law already embodies many such principles. The doctrine of natural justice, for example, is a general principle accepted across legal systems. In Maneka Gandhi v. Union of India (1978), the Supreme Court invoked fairness and reasonableness — principles not explicitly codified in international law, but universally upheld — to interpret Article 21 expansively.

Equally vital is the principle of pacta sunt servanda — agreements must be kept — which guides India’s trade and diplomatic relations. This principle not only reflects India’s commitment to international order but also enhances its credibility in global forums.

Why It Matters for the Judiciary

As global legal obligations increasingly influence domestic law, judges and legal practitioners must be well-versed in the sources of international law. Whether interpreting constitutional provisions, resolving cross-border disputes, or reviewing extradition and trade cases, the ability to navigate treaty provisions, understand customary norms, and apply general principles is essential for ensuring that India remains both a lawful and just global citizen.

In the courtroom of tomorrow, international law will no longer be foreign. It will be foundational. And understanding its sources is the first step in that journey.