International law is a set of rules and procedures which govern the interaction of states and other international actors. It provides normative guidelines on various matters of global importance and includes such subjects as human rights, global environmental issues, world trade, and space law.

International law has its roots in antiquity. For example, in 2100 BCE, Mesopotamian city-states Lagash and Umma signed a peace treaty. Later, polities from the eastern Mediterranean to East Asia concluded numerous international agreements.

The early history of international law was influenced by the diverse cultural and political backgrounds of different nations. During the Renaissance, various factors came together to shape the conceptual framework of international law. A major factor in the development of international law was the introduction of the printing press. This spurred the development of science and notions of individual rights.

In the 18th century, natural rights emerged as a significant element in international politics. They were considered a vital component in both the American and French revolutions.

The 19th century saw a decline in the influence of the naturalist school of thought, with its emphasis on customs and treaties as sources of international law. Increasing political and economic interests, two world wars, and the growth of international organizations weakened the influence of the positivist school.

Throughout the 20th century, European states continued to dominate international law, but international law became truly international by the 1960s and 1970s. This was largely due to the rapid decolonisation of Europe, which brought scores of new independent nations.