What is International Law?

International law is a body of rules, norms and conventions that define what is acceptable behaviour between nations in order to achieve humanity’s most important goals. This includes war, diplomacy, trade, and environmental protection, as well as human rights.

The term ‘international law’ originated in the 19th century and was first defined by Hans Morgenthau as a “body of customary rules”, but it has evolved significantly since then. It is no longer limited to the relations between States; it also applies to international organisations, international bodies and non-State entities.


International Law is a body of rules, norms, and conventions that define what is acceptable behaviour in order to achieve humanity’s most important goal – peace. It is based on the Latin concept of pacta sunt servanda (agreement must be kept).

This definition covers a wide range of areas of law, including state immunity, foreign relations, international organisations, the laws of war, international crimes and their prevention, and the interface between domestic and international legal systems. It is a rapidly evolving area of study that has been transformed by the rapid decolonisation of the world in the 1960s and 1970s.

Modern developments of international law have led to a proliferation of agreements on matters as diverse as nuclear proliferation, climate change, outer space, trade and fishing rights, the treatment of diplomats and much more. Citizens around the world benefit daily from these rules, which are enshrined in treaties between governments and organisations like the United Nations.

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