There are several sources that regularly track major industries. For industry segments or smaller industries' information, IBIS and periodical articles may be the only source
The federal government developed a numerical coding system to identify what a company does. Many of the company databases allow a search using a NAICS or SIC code; this can be an easier way to search for companies within the same industry. Standard Industrial Classification (SIC) is a 4 digit code that identifies an industry. This code was developed in 1937 by the U.S. Government, the last volume was published in 1987. North American Industry Classification System (NAICS) is a 2-6 digit classification code that identifies an industry according to economic activity in Canada, Mexico and the U.S. There are 20 classification sectors. It was developed during the 1990’s to replace SIC codes. A Research Guide with more information on these codes can be found here: NAICS & SIC Codes.