Public International Law (or international public law) concerns the treaty relationships between the nations and persons, which are considered the subjects of International Law. Norms of international law have their source in either:

• Custom, or customary International Law (consistent state practice accompanied by opinio juris),
• Globally accepted standards of behaviour (peremptory norms known as jus cogens), or
• Codifications contained in conventional agreements, generally termed treaties.

Article 13 of the United Nations Charter obligates the UN General Assembly to initiate studies and make recommendations, which encourage the progressive development of International Law and its codification. Evidence of consensus or state practice can sometimes be derived from intergovernmental resolutions or academic and expert legal opinions (sometimes collectively termed soft law).