AIM (formerly the Alternative Investment Market) is a sub-market of the London Stock Exchange that was launched on 19 June 1995. It allows smaller, less-viable companies to float shares with a more flexible regulatory system than is applicable to the main market.
At launch, AIM comprised only 10 companies valued collectively at £82.2 million. By 2017, over one thousand companies comprise the sub-market, with an average market cap of £80 million per listing. AIM has also started to become an international exchange, often due to its low regulatory burden, especially in relation to the US Sarbanes–Oxley Act (though only a quarter of AIM-listed companies would qualify to be listed on a US stock exchange even prior to passage of the Sarbanes–Oxley Act). As of December 2005, over 270 foreign companies had been admitted to the AIM.
The FTSE Group maintains three indices for measuring the AIM, which are the FTSE AIM UK 50 Index, FTSE AIM 100 Index, and FTSE AIM All-Share Index.