International law is an area of legal theory that deals with the rules that govern relations between states. It includes laws that deal with international crimes, state immunity, and international peace. It also covers the rights of aliens and groups, as well as the rights of individuals within a state.

Traditionally, international law centered on norms of conduct during wartime. However, as the modern world developed, the study of international law changed. The introduction of the printing press, along with the rise of European powers, challenged scholars to develop conceptual frameworks.

The study of international law shifted away from the core concern of law of war towards commercial treaties. New international law was created through consensus-building processes, often with the participation of both countries.

The idea of a permanent international court was first proposed at the United Nations in 1948. The creation of the International Court of Justice has helped address many disputes. Many developing nations support the UN Charter and insist on the non-interference in their internal affairs.

International law has been shaped by the political philosophy of ancient Greece. In addition, there were important contributions from the Byzantine Empire, as well as ancient Israel. Ancient Israel had rich cultural traditions, which provided valuable insight into the development of international law.

One of the earliest texts of international law is De jure belli ac pacis by Hugo Grotius. It is a comprehensive study of treaties. A few years later, Bartolo da Sassoferrato, an authority on Roman law, published his own work, The Law of War and Treaties.