The NASDAQ 100 is an index composed of 100 of the largest companies listed on the NASDAQ stock exchange, which is the second largest stock exchange in the world after the New York Stock Exchange in terms of market capitalization. The companies included in this index range across a variety of industries such as technology, communications, biotechnology, media, and services. The NASDAQ 100 was first calculated on January 31, 1985, by NASDAQ and is a market capitalization-weighted index. This index has served as a good reference for investors looking to understand how the stock market performs without the financial services companies, given that the index excludes financial companies.