The FTSE All-Share Index, originally known as the FTSE Actuaries All Share Index, is a capitalisation-weighted index, comprising around 600 of more than 2,000 companies traded on the London Stock Exchange. By weighting companies based on their market capitalisation, the index ensures that companies with larger market capitalisations have a greater influence on the index's performance. Since 29 December 2017 the constituents of this index totaled 641 companies. The FTSE All-Share is the aggregation of the FTSE 100 Index and the FTSE 250 Index, which are together known as the FTSE 350 Index, and the FTSE SmallCap Index. The index is maintained by FTSE Russell, a subsidiary of the London Stock Exchange Group. It aims to represent at least 98% of the full capital value of all UK companies that qualify as eligible for inclusion. The index base date is 10 April 1962 with a base level of 100. Wikipedia