The FTSE 100 is a stock market index consisting of the 100 companies with the largest market capitalization listed on the London Stock Exchange (LSE). The index is one of the key indicators of UK stock market performance, reflecting the economic health of large companies operating in sectors such as banking, energy and pharmaceuticals.

The FTSE 100 was launched in 1984 by the Financial Times and the London Stock Exchange. The index includes large companies with significant international coverage, such as BP, HSBC and GlaxoSmithKline, so movements in the index are influenced not only by UK economic conditions, but also by global dynamics.

The weight of each company in the index is determined by its market capitalization value, with large-cap companies having a greater impact on the movement of the index.
The index is updated regularly, with companies that have decreased in capitalization being replaced by new companies that meet the criteria. The FTSE 100 is often used by investors and analysts to assess market trends, as well as by fund managers to benchmark the performance of their investments.