A Standard Industrial Classification (SIC) code is a four-digit numerical code that categorizes the industries that companies belong to based on their business activities. The SIC codes were created by the U.S. government in 1937 to classify and analyze economic activity across various industries and government agencies, and to promote uniformity in the presentation of statistical data collected by various government agencies. Every company has a primary SIC code that indicates its main line of business. The first two digits of the SIC code identify the major industry group, the third digit identifies the industry group, and the fourth digit identifies the specific industry.

SIC codes are used by businesses and government agencies in a number of ways. Companies use them to identify companies within specific industries for marketing purposes, and to focus their marketing efforts on the industries that generate the highest return on investment. Government agencies use them to classify and analyze economic activity across various industries and to promote uniformity in the presentation of statistical data collected by various government agencies.

Although the SIC codes have been replaced by the North American Industry Classification System (NAICS) codes as the official industry classification system of the United States, many organizations still use SIC codes today. Therefore, it is important to be familiar with both the NAICS codes and SIC codes when doing business research.