The following brief guides are available under the How to find... tab above:
How to find a company's NAICS (North American Industry Classification System) or SIC (Standard Industrial Classification) numbers:
Ritter Library has two databases which provide NAICS codes for public corporations and larger private companies.
Business Source Complete lists NAICS and SIC numbers for public corporations.
Mergent Online lists primary and numerous secondary NAICS and SIC numbers for each company.
If you are researching a smaller private company, try Reference USA, available through Cleveland Public Library. You will need a CleveNet or Greater Access library card (available through Cleveland Public Library) in order to access this resource.
The official websites for searching the North American Industry Classification System (NAICS) and the Standard Industry Classifications (SIC) provide complete descriptions of the classification numbers.