Picture this. You’re reading about a tiny company that makes medical sensors. Fine. Then you notice its shares trade in London, not New York, and there’s a strange tag next to the name: AIM.
Never seen it before? Most Americans haven’t.This is the AIM market, and it’s where London houses its smaller and newer businesses. Join us on this journey and learn everything about it and the precautions you need to take before you start investing.
What is the AIM market?
AIM is a part of the London Stock Exchange. AIM was initially referred to as Alternative Investment Market. There are many who call it that even today. In brief, it is a stock market meant for small companies. The AIM was launched on June 19, 1995 when the London Stock Exchange discontinued its Unlisted Securities Market.
Compare it with a mall.The big department stores sit in the main market. AIM is the little wing with the new shops, some of which will be around in ten years and some of which won’t. Same roof. Different rules.
Why bother? A small company needs money to grow, and selling shares is one way to get it. AIM makes that easier and cheaper than the main market does. For you, that means a chance to buy in early. Or to lose your shirt early. Both happen.Some numbers. In 2007 about 1,694 companies were on AIM, worth around £97 billion all together, says the law firm Osborne Clarke. Then the financial crisis hit, and that value dropped fast. By the end of 2023 the total was about £78.96 billion (roughly $100 billion), per this Baker McKenzie guide to AIM.
How the AIM market works
Every AIM company has to hire a nominated adviser. Everyone calls it a nomad. It’s a finance firm the London Stock Exchange has approved, and its job is to check a company is ready before it lists and keep an eye on it afterward. A coach who never leaves the sideline, basically.
Trades go through the exchange’s own systems, so the same watching applies as on other London markets. There are also market makers, firms that post a buy price and a sell price all day long. Each AIM company has at least two. That’s what lets you buy or sell without hunting for another person to take the other side.Rules are lighter here. They lean on broad principles rather than a thick checklist. Cheaper for the company, sure. But it hands you more homework. Nobody’s going to do it for you.
AIM market vs. the main market
Start with size. The average AIM company was worth about £80 million as of 2021, which is small. Main market companies tend to be a lot bigger and a lot older.
Next, the rules. AIM is what’s called an exchange-regulated market, a lighter setup than the main market’s UK regulated status. Less paperwork for the company, less built-in protection for you. We don’t think that’s automatically bad. It’s a trade, and you should know you’re making it.And risk. Small companies can shoot up. They can also vanish. Want steady, boring returns? An index fund is probably a better fit. Like bigger swings with a small slice of your money? AIM might be worth a peek.
Why companies pick the AIM market
Mostly cash. Selling shares can pay for a new product or the purchase of a rival. A listing also puts a public price tag on the business and spreads ownership around.
The exchange designed AIM for small, growing companies, so the entry rules and the ongoing rules were built to fit them, according to guidance on nibusinessinfo.co.uk. And it isn’t only British firms. Companies from many countries list there.
Risks of the AIM market for investors
Small firms fail more than big ones. That’s just how it goes. Plenty of AIM companies lose money for years while they build something, and some never make a profit. Fine for a young business, but it means the share price is riding on hope, not earnings.
Then there’s trading volume. Fewer people trade these shares, so the gap between what buyers offer and what sellers want can get wide. Sell in a hurry and you could get less than you figured.Also, almost nobody’s watching. Big companies have dozens of analysts writing about them. A tiny AIM company might have none. You’ll be reading the reports yourself.
Critics haven’t been gentle. One commentator once said AIM felt like a casino. The London Stock Exchange fired back that fewer than 2% of AIM companies go into liquidation or administration in a year. Honestly, both sides have a point. Most companies make it through a given year, but any one stock can still fall off a cliff.Our view? Keep AIM stocks as a small side bet. Never the foundation of your plan.
Can US investors buy AIM stocks?
Often, but not always. Some US brokers offer London shares, and plenty don’t. Look at your broker’s list of foreign markets first, before you get attached to a stock.
A few catches. Prices are in British pounds, so the exchange rate can help you or hurt you. London closes around midday New York time, so an afternoon order may sit until the next day. Foreign trades can come with extra fees and tax paperwork too, so ask a tax pro how your gains would be handled. Want more beginner help? See our AIM market and stock investing guides.
What is changing in the AIM market?
In April 2025 the London Stock Exchange put out a paper called Shaping the Future of AIM. It asked the public how to grow the market and make shares easier to trade. One idea: let companies with two classes of shares list. Rules shift, so check the exchange’s site for the latest.
Your next step
Start small. Really small.Select an AIM listed company that interests you and go through their recent reports. How much cash do they have? Are they profitable? How frequently are they traded? Note down why you wish to purchase their stocks and what will make you offload them. Select an amount which you can afford to lose.
This information is only general. Discuss with a qualified professional regarding your personal circumstances. Read more guides like this AIM market explainer on our blog.
FAQ
What does AIM stand for?
AIM stands for Alternative Investment Market. The London Stock Exchange mostly uses the short name now. It’s the exchange’s market for small and growing companies.
Is the AIM market riskier than the main market?
Usually, yes. AIM companies are smaller and younger, and their shares trade less often. That can mean bigger price swings. It doesn’t mean every AIM stock is bad. It just means you should size your bets with care.
Is the AIM market part of the London Stock Exchange?
Yes. The exchange runs it as one of its equity markets, right next to the Main Market.
How many companies are on the AIM market?
It changes over time. The count hit a high of 1,694 in 2007, and there were 821 as of May 2021. Check the exchange’s website for today’s number.