Established in the US in 1937, Standard Industrial Classification (SIC) codes are used to classify types of industry. Other countries and regions have adopted and adapted SIC. The US replaced SIC with NAICS (North American Industry Classification System) in 1997. The EU uses NACE (nomenclature statistique des activités économiques dans la communauté européenne) and there is an international version maintained by the UN (ISIC).
The codes have changed over the years, largely to ensure new industries have a place in the scheme (software development did not exist in 1937). Concordance tables allow users of the various systems map between them. Governments generally require companies to self-classify on tax returns.