Index
A number that summarises the performance of a defined group of stocks.
In short
As of 5 October 2026An index is a figure that sums up the performance of a defined group of stocks in one number, such as the 40 stocks in the DAX. An index provider sets the members using fixed rules and reviews the composition regularly. You cannot invest in an index directly, but you can buy an ETF that tracks it.
An index works like a thermometer for a market. It combines the prices of many stocks into a single number, for example all 40 members of the DAX.
An index provider decides which companies belong, using fixed rules such as size and trading volume. The line-up is reviewed and adjusted regularly.
You cannot invest in an index directly, but an ETF can replicate it. Example: the DAX level on its own says little. What matters is how it changes over time.
Related terms
Sources
As of 5 October 2026 · Educational content, not investment or tax advice.