The FTSE100 (also known as the UK100) is an index comprising shares of the 100 biggest firms, by market capitalization, on the London Stock Exchange (LSE). FTSE is short for Financial Times Stock Exchange based on the two companies that started the index, the Financial Times and the London Stock Exchange. To be measured on the UK100, a company must be listed on the LSE and it must be listed in pounds. The market capitalization of each company is analyzed quarterly, and the index is adjusted as necessary.