Industry classification systems are created to promote data comparability. NAICS (current version) and SIC (older version) are the most widely used in the United States. You can search by classification codes to find information on industries or sectors in many books, databases, and government websites. However, NAICS and SIC focus on broader industry activities and may not have a specific code for niche/emerging industries. Many databases also have their own classification systems.
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 codes are assigned by different research firms and therefore each company may have different codes in different databases.
Older system (doesn't cover industries that emerged after 1987). However, a company must declare its primary SIC in Form S-1 when filing to go public.
Industry Web Resources:
Market Web Resources: