The Unlisted Securities Market (USM), which ran from 1980 to 1996, was a stock exchange

Stock exchange

A stock exchange is an entity that provides services for stock brokers and traders to trade stocks, bonds, and other securities. Stock exchanges also provide facilities for issue and redemption of securities and other financial instruments, and capital events including the payment of income and...

 set up by the London Stock Exchange

London Stock Exchange

The London Stock Exchange is a stock exchange located in the City of London within the United Kingdom. , the Exchange had a market capitalisation of US$3.7495 trillion, making it the fourth-largest stock exchange in the world by this measurement...

 to cater for companies too small to qualify for a full listing.

The USM allowed companies to be traded which did not have the full three year trading history required by the main market, or which wished to float less than 25 percent of their share capital. The USM allowed as little as 10% to be floated.

The Alternative Investment Market

Alternative Investment Market

AIM is a sub-market of the London Stock Exchange, allowing smaller companies to float shares with a more flexible regulatory system than is applicable to the main market....

(AIM) was set up in June 1995. The USM no longer accepted new introductions, and companies which were already quoted on the USM had twelve months to decide either to move the quotation to AIM, or to delist.