The DAX (Deutscher Aktienindex (German stock index); German pronunciation: [daks] (listen)) is a stock market index consisting of the 40 major German blue chip companies trading on the Frankfurt Stock Exchange. It is a total return index. Prices are taken from the Xetra trading venue. According to Deutsche Börse, the operator of Xetra, DAX measures the performance of the Prime Standard’s 40 largest German companies in terms of order book volume and market capitalization. DAX is the equivalent of the UK FTSE 100 and the US Dow Jones Industrial Average, and because of its small company selection it does not necessarily represent the vitality of the German economy as a whole.

The L-DAX Index is an indicator of the German benchmark DAX index's performance after the Xetra trading venue closes based on the floor trading at the Börse Frankfurt trading venue. The L-DAX Index basis is the "floor" trade (Parketthandel) at the Frankfurt stock exchange; it is computed daily between 09:00 and 17:45 Hours CET. The L/E-DAX index (Late/Early DAX) is calculated from 17:55 to 22:00 CET and from 08:00 to 09:00 CET. The Eurex, a European electronic futures and options exchange based in Zürich, Switzerland with a subsidiary in Frankfurt, Germany, offers options (ODAX) and Futures (FDAX) on the DAX from 01:10 to 22:00 CET or from 02:10 to 22:00 CEST.

The Base date for the DAX is 30 December 1987, and it was started from a base value of 1,000. The Xetra technology calculates the index every second since 1 January 2006.

On 24 Nov 2020, Deutsche Börse announced an expansion of the DAX from 30 to 40 members and a tightening of rules in response to the Wirecard accounting scandal. The expansion occurred in the 3rd quarter of 2021.