The E.ON share is part of the most important indices, including the DAX, Dow Jones (DJ) Stoxx 50, DJ Euro Stoxx 50, DJ Stoxx Utilities Index and the German dividend index (DivDAX) as well as the DJ Sustainability Index.

The German Stock Exchange, Paris Stock Exchange (SBF), and Dow Jones have collaborated to establish new European stock market indices. Stock market indices measure the price and performance of a basket of shares. Unlike share price indices, performance indices consider dividends and subscription rights in addition to a stock's performance. The Stoxx family of stock market indices comprises the European DJ Stoxx Index, which includes 600 companies from 16 countries across Europe. The DJ Euro Stoxx Index contains the shares of 300 Euroland corporations.

These comprehensive indices were used to establish two blue-chip indices, each containing the shares of 50 companies. Blue chips are a market's largest and most liquid stocks. The DJ Stoxx 50 is a Europe-wide blue-chip index and the DJ Euro Stoxx 50 is a Euroland index. Both were launched in February 1998. E.ON is in both blue-chip indices.

The dividend index DivDAX exists since March 1, 2005 and comprises the 15 DAX companies with the highest dividend yields. The dividend yield is calculated by dividing the dividend paid by the last price of the share on the trading day previous to the payout. DivDAX members are determined simultaneously with the composition of the DAX index on an annual basis.

As of 24 September 2007 E.ON has been admitted to the most important indices for sustainable companies, the DJ Stoxx Sustainability Index (DJSI Stoxx) and the worldwide DJ Sustainability Index World (DJSI World), and is therefore becoming even more attractive to investors focusing on corporate social responsibility. This increasingly important group of investors tends to prefer long-term exposure and expects companies to create sustained value to make their investment particularly forward-looking and safe. The DJ Sustainability Index only selects the best global or European listed companies from specific industries. E.ON is one of only two German companies in the "Utilities" group of DJSI World and DJSI Stoxx. Companies have to earn admission to these indices every year as poor ratings can lead to their expulsion. Furthermore, since 24 September 2004 E.ON has been included in the ASPI (Advanced Sustainable Performance Indices) Eurozone Index.

Since stock market indices are used as a basis for making investment decisions, there is greater worldwide demand for shares contained in key indices.