"The North American Industry Classification System (NAICS, pronounced Nakes) was developed as the standard for use by Federal statistical agencies in classifying business establishments for the collection, analysis, and publication of statistical data related to the business economy of the U.S. "
NAICS (North American Industry Classification System) -- "developed jointly by the U.S., Canada, and Mexico to provide new comparability in statistics about business activity across North America."
Identifying the NAICS for an Industry -- One of the easiest ways to identify the NAICS or SIC for an industry is to look up a company in that industry using one of the business databases. The descriptive information about the company almost always includes a listing of the industry or industries in which the company is engaged.
Changes in NAICS - Comparing Classifications from Different Years
NAICS has been very slowly replacing the Standard Industrial Classification (SIC) in various commercial resources since 1997. The changes in categories and groupings of industries between SIC and NAICS were extensive and can make it very difficult to compare data longitudinally. Some business sources still include SIC numbers for use in comparing with older data.
You can find detailed descriptions of the direct relationships between classification systems from here:
SIC (Standard Industrial Classification) Manual
North American Product Classification System (NAPCS) - "In February 1999, the statistical agencies of Canada, Mexico, and the United States launched a joint multi-phase initiative to develop a comprehensive demand-oriented product classification, known as the North American Product Classification System (NAPCS). Work to date has focused on the products produced by service industries in 12 NAICS sectors 48-49 through 81."