Some information providers organize the data by NAICS and SIC classification codes. NAICS (North American Industry Classification System) is the official classification system used in the U.S. It uses a hierarchical system of up to six digits to group together establishments that use the same or similar processes to produce goods or services. Most government agencies, including the Census Bureau, report business activity using NAICS.
SIC codes, first adopted in the 1930s, are still used by the Securities & Exchange Commission and some private data sources. Thus, it is still important to find the SIC code applicable to the industry you are researching. It uses a hierarchical system of up to four digits to classify establishments according to their primary economic activity.
Most libraries have print copies of the North American Industry Classification System and the Standard Industrial Classification Manual. In Joyner Library, copies are kept at the Reference Desk and in the Business Reference area. Classifications can also be found online:
NAICS: http://www.census.gov/eos/www/naics/
SIC: https://www.osha.gov/pls/imis/sic_manual.html