The Moroccan-American Treaty of Peace and Friendship, sealed by Sultan Mohammed III.
The Hittite version of the Treaty of Kadesh, among the earliest extant examples of an international agreement.
The signing of the Geneva Conventions in 1949. A country’s signature, through plenipotentiaries with "full power" to conclude a treaty, is often sufficient to manifest an intention to be bound by the treaty.
The International Court of Justice is often called upon to aid in the interpretation or implementation of treaties.
A treaty delegation of the Mdewakanton and Wahpekute indigenous tribes to Washington, D.C. (1858).

Sources of international law include treaties, international customs, general widely recognized principles of law, the decisions of national and lower courts, and scholarly writings.

- Sources of international law

Treaties serve as primary sources of international law and have codified or established most international legal principles since the early 20th century.

- Treaty
The Moroccan-American Treaty of Peace and Friendship, sealed by Sultan Mohammed III.

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The Hittite version of the Treaty of Kadesh, among the earliest extant examples of an international agreement.

International law

Set of rules, norms, and standards generally recognized as binding between nations.

Set of rules, norms, and standards generally recognized as binding between nations.

The Hittite version of the Treaty of Kadesh, among the earliest extant examples of an international agreement.
Hugo Grotius' De jure belli ac pacis, is considered one of the foundational texts of international law. (Pictured is the title page from the second edition of 1631).
A portrait of the Dutch jurist Hugo Grotius (alias Hugo de Groot)
Sir Alberico Gentili is regarded as the Father of international law.
The First Geneva Convention (1864) is one of the earliest formulations of international law

The sources of international law include international custom (general state practice accepted as law), treaties, and general principles of law recognized by most national legal systems.

Emblem of the International Court of Justice

International Court of Justice

One of the six principal organs of the United Nations (UN).

One of the six principal organs of the United Nations (UN).

Emblem of the International Court of Justice
The Peace Palace in The Hague, Netherlands, seat of the ICJ
Audience of the "Accordance with International Law of the Unilateral Declaration of Independence by the Provisional Institutions of Self-Government of Kosovo"

The ICJ is the only international court that adjudicates general disputes between countries, with its rulings and opinions serving as primary sources of international law.

2) Compromissory clauses in a binding treaty. Most modern treaties contain such clauses to provide or dispute resolution by the ICJ. Cases founded on compromissory clauses have not been as effective as cases founded on special agreement, since a state may have no interest in having the matter examined by the court and may refuse to comply with a judgment. For example, during the Iran hostage crisis, Iran refused to participate in a case brought by the US based on a compromissory clause contained in the Vienna Convention on Diplomatic Relations and did not comply with the judgment. Since the 1970s, the use of such clauses has declined; many modern treaties set out their own dispute resolution regime, often based on forms of arbitration.

The Hittite version of the Treaty of Kadesh, among the earliest extant examples of an international agreement.

Customary international law

Aspect of international law involving the principle of custom.

Aspect of international law involving the principle of custom.

The Hittite version of the Treaty of Kadesh, among the earliest extant examples of an international agreement.

Along with general principles of law and treaties, custom is considered by the International Court of Justice, jurists, the United Nations, and its member states to be among the primary sources of international law.