brief introduction to international law


International law is the body of law that encompasses the rules and relationships between sovereign states, international organisations and international relations (public international law) and between private individuals (private international law).

The major players of public international law are considered to be:

  • The heads of state and the bodies involved in foreign policy in government (ministry of foreign affairs, state departments, military).
  • Inter-governmental organisations (IGOs) such as the United Nations and European Union.
  • Subject orientated organisations (World Health Organisation, International Monetary Fund, international Civil Aviation Organisation, United Nations Educational, Scientific and Cultural Organisation (UNESCO).

There are four main sources of international law as identified in Article 38 of the Statute of the International Court of Justice (ICJ):

1. International conventions (treaties) establish written rules that are signed by states which are binding and governed by international law.

2. International custom is a general unwritten rule that is binding on all states. It is based on assumed consent evidenced by the behaviour of states and a belief by states that it is a legal obligation (opinio juris).

3. General principles of law recognised by civilised nations that is not open to appeal or challenge. This includes the use of force except in self-defence, good faith and impartiality of judges.

4. Judicial decisions and the teachings of the most highly qualified publicists. This means the law of a state as a determination for international law. Domestic courts may play a subsidiary role in helping determine the rules of international law. It also includes scholarly writing on international law as a source of determination.



International law is attributed to the Dutch diplomat and jurist Hugo Grotius (also known as Hugo de Groot). In particular, the idea of there being a society of states.

The two World Wars accelerated the appetite and need for international law. The formation of the League of Nations resulted from World War I. The failure of the Treaty of Versailles and the end of World War 2 replaced the League of Nations to the United Nations.

Problem of international law

The main weakness of international law is that there is no world police or army to enforce compliance in the law. States can ignore principles and treaties. The value of compliance in international law is rooted in national self-interest. If one state breaks the rules, another state may do the same.