An industry is a group of companies involved in the same economic activity. Until recently, these economic activities were designated by a system of numeric codes called the Standard Industrial Classification (SIC) System. This system, developed by the Federal government more than fifty years ago, assigned a four-digit number to a specific industry.

The North American Industry Classification System (NAICS) is in the process of replacing the SIC System. NAICS is an improvement over the SIC system. SIC codes consisting of four digits will be replaced by six-digit NAICS numbers. In addition, some 350 new industries are being separately recognized for the first time with NAICS.

Consult the U.S. Bureau of Census NAICS site for a list of NAICS codes, tables showing correspondence between NAICS and the SIC system, and other information on how NAICS differs from the SIC System.