Public companies are categorized by major stock sectors.
  • Agriculture
  • Banking
  • Basic Materials
  • Capital Goods
  • Chemicals
  • Communications
  • Construction
  • Consumer Non-Durables
  • Clothing
  • Conglomerates
  • Consumer Durables
  • Credit
  • Drugs
  • Electronics
  • Entertainment
  • Energy
  • Food and Beverage
  • Hardware
  • Healthcare
  • Investing
  • Insurance
  • Information Technology
  • IT Services
  • Media
  • Medical Facilities
  • Metals and Mining
  • N/A
  • Real Estate
  • Services
  • Software
  • Technology
  • Transportation
  • Utilities

Ten most popular sectors (a different breakdown):
  • Consumer Discretionary
  • Consumer Staples
  • Energy
  • Financials
  • Health Care
  • Industrials
  • Information Technology
  • Materials
  • Telecommunication Services
  • Utilities

U.S. Standard Industrial Classification (SIC)

SIC codes are a standard series of four-digit codes created by the U.S. government in 1937 for categorizing business activities. In 1997, the use of SIC codes was replaced in most (but not all) capacities by a six-digit code called the North American Industry Classification System (NAICS). The codes are used to promote better communication across business sections and between countries. One major government department that still uses SIC codes is the Securities and Exchange Commission (SEC). The SIC codes are listed in a business's electronic data gathering, analysis and retrieval system (EDGAR) filings in order to indicate the industry to which the company belongs. (Meta data: RDF/OWL Ontology)

NAICS (North American Industry Classification System)

A new business classification system developed through a partnership between the United States, Canada and Mexico. This system allows statistics to be compared for all business activity across North America. All companies are separated into industries defined by businesses that use similar production processes. The NAICS was created to replace the U.S. Standard Industrial Classification (SIC) system to modernize it, so that it would be able to relate to the constantly changing economy. The new system also allows for better comparability between all North American countries, which is important because of the increased trade between NAFTA countries. To ensure that the NAICS will be able to keep pace with changing economic conditions it will be reviewed every 5 years.

All of these different classification systems should be (could be) cross referenced to one another. (Of course you can purchase a cross reference) ***

Of course, an even better approach would be a global system of industry classification codes!