The NASDAQ-100 is a stock market index of 100 of the largest domestic and international non-financial companies listed on the NASDAQ stock exchange, it is a modified market value-weighted index; the companies weights in the index are based on their market capitalization, with certain rules capping the influence of the largest components. It does not contain financial companies, and includes companies incorporated outside the United States; both of these factors differentiate this index from the S&P 500 and the Dow Jones Industrial Average.
The NASDAQ-100 began on January 31, 1985 as a way for the Nasdaq Stock Market to support enhanced media coverage for itself. The index was introduced the same day as the NASDAQ Financial-100 Index and as a result, financial companies were, and still are, excluded from the NASDAQ-100. The base price of the index was initially set at 250, but when it closed near 800 on December 31, 1993, the base was reset at 125 the following trading day, leaving the halved NASDAQ-100 price below that of the more commonly known NASDAQ Composite.
