FTSE 100 Index
The FTSE 100 Index is the most widely-quoted and 'popular' index for tracking the London stockmarket.
The FTSE 100 contains the shares of the top 100 U.K. companies ranked by market capitalisation. It's jointly sponsored by the Financial Times, the London Stock Exchange, and the Institute and Faculty of Actuaries and marketed by a company called 'FTSE International'.
The 'FTSE' is a market capitalisation-weighted index, re-weighted every day. During the day, it is calculated every minute.
Shares enter and leave the index every quarter. Additions and deletions are performed strictly in accordance with a set of rules supervised by the FT-SE Actuaries Share Indices Steering Committee, an independent body.