The FTSE 100 Index (UKX) is a market-capitalisation weighted index of the 100 blue chip companies listed on London Stock Exchange which are most highly capitalised and pass screening for size and liquidity. Promotions and demotions from this index occur quarterly in March, June, September and December. Although, the index consists of 100 companies, there are 101 listings, as Royal Dutch Shell has both A and B class shares listed.