The North American Industry Classification System (NAICS) groups establishments into industries based on the similarity of their production processes. The system was introduced in 1997 to replace the Standard Industrial Classification (SIC) and is used in Canada, the United States, and Mexico. There are 20 sectors and 1,065 industries in the 2012 NAICS United States.
NAICS uses a six-digit coding system to identify particular industries. Industries are placed in a hierarchy of sector, subsector, industry group, NAICS industry, and national industry.
For example:
31 Manufacturing (sector)
311 Food Manufacturing (subsector)
3119 Other Food Manufacturing (industry group)
31191 Snack Food Manufacturing (NAICS industry)
311911 Roasted Nuts and Peanut Butter Manufacturing (national industry)
Because of its hierarchical nature, researching industries using the NAICS codes makes it easier to understand how industries are related and how they can be broken down. When you are researching industries this hierarchy helps you to understand what you are searching for. Are you interested in food manufacturing? Do you want to find information just about peanut butter manufacturing? Or, are you interested in all manufacturing?
Many government publications and business databases offer the option to search by NAICS code. Doing so is a great way to ensure that you are finding all of the relevant businesses for the industry that you are researching. Both the NAICS website and the print edition contain detailed descriptions of each industry, which can also help guide your research.
North American Industry Classification System by 
Standard Industrial Classification Manual : 1987 by