Industry Classification codes are used to define or describe an industry and allow for the searching and comparison of companies across an industry.
NAICS
The North American Industry Classification System (NAICS) is the standard used by Federal statistical agencies to classify business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy. To retrieve the NAICS number for the industry you are researching use the keyword search box on the left. This number will allow you to search for your industry in a variety of other databases without pinpointing specific companies that are aligned with the industry.
Can a business have more than one NAICS code?
The U.S. Census Bureau assigns and maintains only one NAICS code for each establishment based on its primary activity (generally the activity that generates the most revenue for the establishment), but since other agencies and organizations have adopted NAICS for use in programs that are not statistical (e.g., regulatory activities and procurement), they may allow for more than one NAICS code per establishment.
For more information on this subject and NAICS codes in general, select the NAICS link above and navigate to the FAQ page.
SIC
The Standard Industrial Classification (SIC) system was the precursor to the NAICS. Some databases still use the SIC as an industry identifier. SIC only includes US industries, while NAICS includes North American industries (Canda, Mexico and the United States).
SIC /NAICS Conversion Table
This web page facilitates an easy conversion from SIC to NAICS through the use of Microsoft Excel spreadsheets.
GICS
The Global Industry Classification Standard is an industry taxonomy developed by MSCI and Standard & Poor's (S&P) for use by the global financial community. The GICS structure consists of 10 sectors, 24 industry groups, 67 industries and 156 sub-industries.
ISIC Rev. 4:
International Standard Industrial Classification of All Economic Activities, Rev.4 is the United Nations system for classifying data according to kind of economic activity in the fields of production, employment, gross domestic product and other statistical areas.
National Classifications:
The United Nations provides access by region and country to the activity and product based classifications systems used around the world. This information is collected through the UN questionnaire on country practices in classifications and similar sources.
For help with using the database, please use the IBISWorld Getting Started guide linked below
Market Intelligence (Export.gov)
Export.gov is the U.S. Government's portal to international trade and market research resources. The Market Intelligence Library contains more than 100,000 industry and country-specific market reports, including Country Commercial Guides ("doing business" guides), Industry Reports and Top Market Reports. Export.gov is managed by the U.S. Department of Commerce's Commercial Service in collaboration with other Federal agencies that offer export assistance programs and services.
Financial Ratios are generally calculations based on company accounts and other sources (e.g. stock exchange share prices) designed to indicate the profitability or other financial aspects of a business, such as returns on net assets, price-earning ratio and stock sales ratio. Financial ratios have been used for centuries as benchmarks for gauging a companies viability and for comparing its performace to competitors in its primary industry classification.
Almanac of Business and Industrial Financial Ratios by 
RMA Annual Statement StudiesCounty Business Patterns
An annual series that provides sub-national economic data by industry. County Business Patterns covers most of the country's economic activity.
Economic Census
The Economic Census profiles the US economy every 5 years, from the national to the local level. Reports are available for all geographic areas and sectors, including retail trade, wholesale trade, construction, and manufacturing.