Conventional international law refers to rules governing relations between states and international organisations that arise from written agreements, principally treaties and conventions, rather than from customary international law. In legal practice in the UK and Ireland, it is used to distinguish treaty-based obligations from unwritten customary norms or general principles of international law. The term itself is descriptive rather than a defined statutory expression, but it is widely used in public international law texts, case law and diplomatic practice across England and Wales, Scotland, Northern Ireland and Ireland, with no material difference in meaning between these jurisdictions. Conventional international law is created through the negotiation, signature, ratification and entry into force of international treaties (such as the European Convention on Human Rights or EU treaties pre-Brexit). Its practical significance lies in determining: which international obligations bind a state; how they should be interpreted (often by reference to the Vienna Convention on the Law of Treaties); and how they interact with domestic constitutional and legislative frameworks, including doctrines on incorporation, dualism and parliamentary supremacy.