The North American Industry Classification System (NAICS) is used to organize industry information. It's designed to produce common industry definitions for Canada, Mexico, and the United States. It is a hierarchical classification system, offering five levels of detail. Codes are assigned to an industry based on products and services provided by the industry.
Industries are represented by a six-digit number. The first two digits designate the economic sector: manufacturing, agriculture, wholesale, retail, professional services, etc. The subsequent digits designate subsectors and industry groups.
Each digit in the code is part of a series of progressively narrower categories.
44 - Retail
448 - Clothing and Clothing Accessories Stores
4481 - Clothing Stores
448140 - Family Clothing Stores
The Standard Industrial Classification (SIC), an earlier U.S. system, is still used by some sources.
To find industry codes for a specific company, search for a company profile in a company directory. Note that many companies operate in more than one industry (e.g. have multiple lines of business) and may have more than one code.