ICS refer to a system through which a company is classified into an "Industry" on the basis of stated parameters. In simple words, it refers to grouping of homogeneous companies under one head. One point to be remembered here is that industry classification has been a long-standing problem in the financial research. As of today, different types of classification system prevail in the financial world, Standard Industry Classification System (SICS), North American Industry Classification System (NAICS), Global Industry Classification Standard (GICS), Industry Classification Benchmark (ICB) to name a few. Even countries too follow a different system or set of rules to classify a company.

Standard Industry Classification (SIC):

The Standard Industrial Classification (abbreviated 'SIC') is a United States government system for classifying industries by a four-digit code. Established in the 1930s, it is being supplanted by the six-digit North American Industry Classification System, which was released in 1997; however certain government departments and agencies, such as the U.S. Securities and Exchange Commission (SEC), still use the SIC codes.

NAICS is the North American Industry Classification System. NAICS is used by business and government to classify and measure economic activity in Canada, Mexico and the United States. It is in the process of replacing the older Standard Industrial Classification (SIC) codes; however certain government departments and agencies, such as the U.S. Securities and Exchange Commission (SEC), still use the SIC codes.

The NAICS numbering system is a six-digit code. The system is designed to be compatible with the United Nations Statistical Office's International Standard Industrial Classification System (ISIC). Work began on NAICS in the U.S. in 1992, when the Office of Management and Budget (OMB) formed the Economic Classification Policy Committee (ECPC), staffed by the Bureau of Economic Analysis (BEA), the Bureau of Labor Statistics (BLS), and the Census Bureau. NAICS takes into account the huge economic change towards service businesses. The first version is NAICS 1997. The next revision would be in 2007, toward NAPCS.