The term „transnational law“ sometimes gets used to a set of rules that goes beyond the nation-state. The term „international law“ is sometimes divided into international law „public“ and „private“, especially by civil law scholars who want to follow a Roman tradition. Roman jurists would have continued to distinguish juice gentium, the law of nations, and juices inter gentes, from agreements between nations. From this point of view, „public“ international law must cover relations between nation states and covers areas such as contract law, law of the sea, international criminal law, international law of war or humanitarian law, international human rights law and refugee law. On the other hand, „private“ international law, more often referred to as the „conflict of laws,“ concerns whether courts within a country claim jurisdiction over cases with a foreign element and what country law applies. A more recent term is „supranational law,“ which refers to regional agreements, in which the laws of nation states may be considered unheard of when they conflict with a supranational legal system to which the nation is contractually bound. Systems of supranational law arise when nations expressly cede their right to make certain judicial decisions to a common court. The decisions of the common court are directly effective in each State party and take precedence over the decisions of national courts. The European Union is the most important example of an international contractual organisation implementing a supranational legal framework, with the European Court of Justice having the predominance of all member courts in the field of EU law. This definition has led the jurisprudence to define a treaty as an international agreement that meets the following criteria: although States (or more and more international organizations) are generally the only ones to oppose a violation of international law, some treaties, such as the International Covenant on Civil and Political Rights, have an optional protocol that provides for persons who have violated their rights of Member States. , to petition the International Committee on Human Rights. Investment contracts are generally and regularly imposed by individuals or investment institutions. and foreign trade agreements with sovereign governments can be applied internationally.

Ancient Greece, which developed fundamental conceptions of governance and international relations, contributed to the formation of the international legal system; Many of the first peace agreements ever concluded between Greek city-states or with neighbouring states.