The North American Industry Classification System or NAICS is used by business and government to classify and measure economic activity in Canada, Mexico and the United States. The NAICS numbering system is a six-digit code. The first five digits are generally (although not always strictly) the same in all three countries. The last digit designates national industries. The first two digits designate the largest business sector, the third digit designates the subsector, the fourth digit designates the industry group, and the fifth digit designates particular industries.