Secondary legislation refers to legally binding rules made under powers delegated by an Act of Parliament or Act of the Oireachtas, rather than being enacted directly by the legislature itself. It is commonly used to fill in technical detail, implement EU or international obligations, set commencement dates, prescribe forms or fees, and update regulatory regimes without passing a new primary Act. In the UK, secondary legislation (also called “subordinate” or “delegated” legislation) includes statutory instruments, Orders in Council and regulations made by ministers, devolved administrations and certain public bodies under enabling Acts. In Ireland, it similarly covers statutory instruments, regulations and orders made under primary legislation. The term is widely used in legislation, case law and practice, although precise definitions are usually found in context-specific provisions (for example, Interpretation Acts and particular enabling statutes). Across England and Wales, Scotland, Northern Ireland and Ireland, the core concept is consistent: secondary legislation must stay within the scope of the parent Act, is subject to specified parliamentary or Oireachtas scrutiny procedures, and is vulnerable to judicial review if it exceeds delegated powers or breaches constitutional or human rights norms.