A site of special scientific interest (SSSI) in Great Britain, or an area of special scientific interest (ASSI) in the Isle of Man and Northern Ireland, is a conservation designation denoting a protected area in the United Kingdom and Isle of Man. SSSI/ASSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in the United Kingdom are based upon them, including national nature reserves, Ramsar sites, Special Protection Areas, and Special Areas of Conservation. The acronym "SSSI" is often pronounced "triple-S I".

NatureScot is the operating name for the body formally called Scottish Natural Heritage. It is an executive non-departmental public body of the Scottish Government responsible for the country's natural heritage, especially its natural, genetic and scenic diversity. It advises the Scottish Government on nature conservation, and acts as a government agent in the delivery of conservation designations, i.e. national nature reserves, local nature reserves, national parks, Sites of Special Scientific Interest (SSSIs), Special Areas of Conservation, Special Protection Areas and the national scenic areas. It receives annual funding from the Government in the form of Grant in Aid to deliver Government priorities for the natural heritage.