If you want to buy shares in a specific company, you first need to check that the company in question is listed on a stock exchange. The main stock exchange in the UK is the London Stock Exchange and consists of over 1,000 stocks from 100 countries. There are small exchanges such as the AIM Market, which has around 850 companies worth over £104 billion. Once you have chosen a company listed on the London Stock Exchange to buy shares in, you need an account with a stock broker to help with the purchase.