According to the Statute of the International Court of Justice, international custom refers to general practices, customs or practices accepted as law. As the source of international law, international custom was very important before19th century and at the beginning of 20th century, because the compilation of international law there was underdeveloped.

Now, although international treaties are the most important, customary law, as a mechanism, method or process of the formation of international law, can not be ignored.