Major stock market indexes

About this section

When the news says "the market" rose or fell, it usually means an index: a basket of stocks chosen under published rules, summarised as one number. The well-known indexes look similar in a headline, but they are built very differently. The S&P 500 is chosen by a committee and weighted by company size. The Dow Jones Industrial Average holds just 30 stocks and is weighted by share price. The Nasdaq Composite takes nearly everything listed on one exchange, while the Russell 2000 is defined purely by size rank. The MSCI World spans developed countries, and the FTSE 100 covers the largest UK-listed companies.

Each profile on this page starts with a short fact panel — provider, launch date, number of members, weighting method, review schedule and currency — with every item linked to the provider's methodology, fact sheet or official page. Then it explains the rules in plain English and works through an example with made-up numbers, so you can see how weighting or a review rule actually changes the index. We deliberately leave out index levels, past returns and current top holdings, because those change constantly. Nothing here is advice to buy or sell anything; an index is a measuring tool, and funds that track one carry their own costs and risks.