When doing business research, it is useful to obtain the NAICS codes and SIC codes.  

• NAICS (North American Industry Classification System): This "is the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy."
• SIC (Standard Industrial Classification): The industry classification system in which all Federal economic statistics were based on up to 1996. The NAICS system replaced this in 1997.

The links below will help you find the codes for specific types of industries.  You can also find NAICS and SIC codes by looking at the industry information for a company in a database like Mergent Intellect.

It is important to know these codes in order to retrieve statistical information produced by the Census as well as search certain databases by these codes.  For instance you can use it to find industry overviews in databases like First Research and IBISWorld, and identify companies in an industry with a database like Reference Solutions or Mergent Intellect.

You can use NAICS and SIC codes to find Industry reports from IBISWorld and First Research.

Use the NAICS and SIC codes in Mergent Intellect or Reference Solutions to build a list of competitors from a zip code to U.S. city to country level.

In addition, you can search by keyword in IBISWorld and First Research, and by company in Mergent Intellect and Reference Solutions to obtain a NAICS or SIC code.