Sources of International law mean those origins from where it attains its authority and coercive agency.
According to the provisions of the Statute of International Court of Justice there are following sources, on the basis of which Court can decide a case:

Treaties

A treaty is an agreement that Nation states enter into to establish relations with each other and to undertake specific duties, obligations, and rights. The statute states that the Court must resolve any dispute between Nation States based on the provisions of the existing treaty between them.

Customs

Nations commonly observe customs, which are habits and practices. Violating these customs is considered contrary to the courtesy of international behavior.

There are certain practices which the world community observes without any express provisions but because of practice they honor the same. So if there is no treaty between the parties to a dispute then the statute binds the Court to decide the case in the light of such international customs.

General Principals of Law Recognized by Civilized Nations

Many countries have incorporated certain principles of law into their domestic laws due to their universal applicability.

So, in default of any treaty or international custom the statute reveals that the court then shall have to decide the case in the light of such general principles of law as recognized by civilized nations of the world.

Judicial Decisions

Usually the Judicial decisions of the International Court of Justice are not binding and they have no value in the sense that they are related and binding only to that certain case for which they have given. And they cannot be cited as strict reference in any other case. But despite the fact the Statute reveals that in case of default of all the above sources the court shall resort to the prior judicial decisions.

Juristic Works

The jurists or publicists also declares rules by legal philosophy and analogy and also by comparing different legal systems of the world and they also analyze the historical perspectives of the different legal systems of the world. So, as they have devoted their lives for the legal study, they must be deserved to consult in deciding a dispute. In other words, their opinion on a specific question of law weights because of the their valuable experiments and sound study on the topic. So, the statute further reveals that if there is no treaty, legal custom and general principles of law then the Court shall resort to writings of these jurists.

Other Sources

Beside the above sources there are also some other sources of International Law which court can resort for the decision of a case. As for example “Equity” and the resolution by the UN organization.

The statute does not declare these sources for the Court to derive law from them. However, in practice, the courts have observed common and universal principles of equity while deciding cases.

And also the UN organization when passes a resolution on specific subject the Court feels its moral duty to decide the case in the light of such resolution if there is no express provisions for deciding a case.

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