International law is a body of rules, norms and standards that regulate interactions between sovereign states and other legally recognized international actors. It includes laws, treaties, and other legal instruments.

The origins of international law can be traced back to antiquity. Among the earliest examples are peace treaties between Mesopotamian city-states, such as Lagash and Umma (approximately 2100 BCE) or the Hittite version of the Treaty of Kadesh (1258 BCE).

Some of the most important principles of international law are state sovereignty and territorial integrity. These principles mean that a state is free to choose which laws it follows, and that it has a choice over whether to join a treaty.

Another principle is the rule of international law, which is that all civilized nations must follow certain norms of conduct. These include the prohibition of genocide, slavery and the slave trade, wars of aggression, torture and piracy.

Despite its universality, there are many differences in the way that different countries interpret international law. European democracies, for instance, tend to support broad, universalistic interpretations of international law.

International law is a complex field, and there are numerous arguments over how to define and apply it. Some argue that it should be derived from treaties between states, while others think that it should draw on customary law.