The North American Industry Classification System (NAICS) is the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy.
NAICS was developed under the auspices of the Office of Management and Budget (OMB), and was adopted in 1997 to replace the Standard Industrial Classification (SIC) system. If you are doing research and need historical information on an industry, you will need to use SIC codes.