另类投资市场（Alternative Investment Market，简称AIM）是伦敦证券交易所的第二板交易市场，容许小型公司在较主板市场宽松的财务条例下将股份上市。另类投资市场于1995年创立，共为超过2,200间公司募集240亿英镑。宽松的条例包括较少的条例及没有公司市值或发行股票数量的要求。部分在另类投资市场上市的公司其后会转投主板市场，但在近年来更多的公司由主板市场转到另类投资市场，基于另类投资市场让投资者获得更佳的税务优惠及公司不用被重重条例规限。2005年共有40家公司由主板市场转到另类投资市场，而只有两家公司作反向迁移。

AIM (formerly the Alternative Investment Market) 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 launched on 19 June 1995 and has raised almost £24 billion and has helped more than 3,000 small-medium-sized companies raise equity to support their growth. Among these are companies from particularly high-growth areas such as technology, clean-tech and biotech. Flexibility is provided by less regulation and no requirements for capitalisation or number of shares issued. Some companies have since moved on to join the Main Market, although in the last few years, significantly more companies transferred from the Main Market to the AIM (the AIM has significant tax advantages for investors, as well as less regulatory burden for the companies themselves). In 2005, 40 companies moved directly from the Main Market to the AIM, while only two companies moved from the AIM to the Main Market.