International law is derived from agreements between countries, and is often referred to as the Law of Nations. Sources of international law include treaties, custom, and general principles of law recognized by most legal systems. International comity is often an expression of international law and is used to maintain good relations between nations as well as enforce foreign legal judgments. However, the Law of Nations and customary law are not synonymous. The law of international comity differs between states, and is therefore difficult to define.

In the past, the only subject matter of international law was sovereign states, including the Holy See. However, in recent years, various other parties have become relevant, including multinational corporations, individuals, and global commons. International law has a wide range of uses and can regulate all aspects of national law. Some jurisdictions even recognize corporations as parties to international disputes. In many cases, the law of international law requires both parties to abide by the laws of the state where the conflict originated.

Various UN organs are involved in the development, enforcement, and application of international law. The International Law Commission performs classical legal work, while the special committees of the General Assembly and Offices of High Commissioners make practical decisions. There are many more bodies that promote international law and its principles. The International Law Commission is one such body, composed of experts who create reports on issues related to international law. These reports serve as the basis for negotiations of treaties later.