The NASDAQ Composite is a capitalization-weighted index. The calculation of the index involves the calculation of the weighted sum of the products of the closing prices of the securities. This sum is divided by a divisor which reduces the order of magnitude of the result. For a security to be included in the Nasdaq Composite, it must be listed exclusively on the Nasdaq Stock Market, unless the security has been listed at least twice on a non-US market before 2004 and has remained listed continuously.

The index was introduced in 1971, with an initial value of 100. On 17 July 1995 it closed for the first time with a value greater than 1000. During the dot-com bubble the value of the index increased by 400%. On March 10, 2000 it reached the maximum value of 5132.52. In the following period the value suffered a notable decline, reaching 1,108.49 on 10 October 2002. Until 2007 the index saw a reduction in its value. On September 15, 2008, the bankruptcy of Lehman Brothers led the index to record -3.6%, the worst percentage drop in a single session since March 24, 2003.