This page is included in the guide for students taking subjects on public international law.
Primary sources include treaties (conventions), customs and general principles of law. Secondary sources include judicial decisions and doctrines (e.g. decisions made by the International Court of Justice or the United Nations).
A treaty, or convention, is an agreement between two or more states or international organisations (e.g. the Geneva Convention 1864; the International Bill of Human Rights). Historical customary practice may also form part of international law, provided there is evidence the custom is accepted by states as legally binding (e.g. International Court of Justice ruling on Nicaragua v. United States of America (1986)).
Check out this interactive timeline to discover more about this history of international law: The history of international law by Oxford Academic.