The FTSE All-Share Index, originally known as the FTSE Actuaries All Share Index, is a capitalisation-weighted index, comprising around 1000 of more than 2,000 companies traded on the London Stock Exchange. As at June 2011 the constituents of this index totalled 627 companies (source FTSE All Share fact sheet). 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.
To qualify, companies must have a full listing on the London Stock Exchange with a Sterling or Euro denominated price on SETS or SETSmm or a firm quotation on SEAQ or SEATS, and must meet a number of other eligibility requirements.