A Standard Industrial Classification (SIC) code is a four-digit numerical code assigned by the U.S. government that categorizes the industries to which companies belong based on their business activities. The SIC system was established in the United States in 1937 as a method of standardizing industry classification for statistical purposes across agencies. SIC codes are assigned based on common characteristics shared in the products, services, production, and delivery system of a business. The first two digits of the code represent the major industry sector to which a business belongs, while the third and fourth digits describe the sub-classification of the business group and specialization, respectively.

The SIC code for an establishment, which is a unique business with a registered U.S. headquarters, is determined by the industry appropriate for the overall largest product lines of the company or organization of which the establishment is a part. The Social Security Administration assigns SIC codes to businesses based on the descriptions provided by employers under the primary business activity entry on employer ID applications.

SIC codes are used by government agencies, including the SEC, and some companies today, despite having been mostly replaced by the six-digit North American Industry Classification System (NAICS) . The last digit of a SIC code is the most specific identifier of a company, and it further refines the business classification into a very specific business category. For example, SIC code 2050 represents bakery products, while SIC code 2052 represents cookie & cracker manufacturers.

To find a companys SIC code, one can search the 1987 version SIC manual by keyword or access descriptive information for a specified 2, 3, or 4-digit SIC on the Occupational Safety and Health Administration website.