SECURITIES AND EXCHANGE COMMISSION

FORM 6-K

REPORT OF FOREIGN ISSUER

Pursuant to Rule 13a-16 or 15d-16 of
the Securities Exchange Act of 1934

For the month of November, 2004

E.ON AG

E.ON AG
E.ON-Platz 1
D-40479 Düsseldorf
Germany
(Address of Principal Executive Offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F þ     Form 40-F o

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes o     No þ

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b):

January 1 — September 30, 2004

Interim Report III/2004

Interim Report III/2004

E.ON Group Financial Highlights

E.ON Group Key Figures at a Glance

Non-GAAP financial measures: This report contains certain non-GAAP financial measures. Management believes that the non-GAAP financial measures used by E.ON, when considered in conjunction with (but not in lieu of) other measures that are computed in U.S. GAAP, enhance an understanding of E.ON’s results of operations. A number of these non-GAAP financial measures are also commonly used by securities analysts, credit rating agencies, and investors to evaluate and compare the periodic and future operating performance and value of E.ON and other companies with which E.ON competes. Additional information with respect to each of the non-GAAP financial measures used in this report is included together with the reconciliations described below.

E.ON prepares its financial statements in accordance with generally accepted accounting principles in the United States (U.S. GAAP). As noted above, this report contains certain consolidated financial measures (internal operating profit, adjusted EBIT, adjusted EBITDA, net financial position, net interest expense, and free cash flow) that are not calculated in accordance with U.S. GAAP and are therefore considered “non-GAAP financial measures” within the meaning of the U.S. federal securities laws. In accordance with applicable rules and regulations, E.ON has presented in this report a reconciliation of each non-GAAP financial measure to the most directly comparable U.S. GAAP measure for historical measures and an equivalent U.S. GAAP target for forward-looking measures. The footnotes presented with the relevant historical non-GAAP financial measures indicate the page of this report on which the relevant reconciliation appears. The non-GAAP financial measures used in this report should not be considered in isolation as a measure of E.ON’s profitability or liquidity and should be considered in addition to, rather than as a substitute for, net income, cash provided by operating activities, and the other income or cash flow data prepared in accordance with U.S. GAAP presented in this report and the relevant reconciliations. The non-GAAP financial measures used by E.ON may differ from, and not be comparable to, similarly titled measures used by other companies.

2

Interim Report III/2004

Contents

3

Interim Report III/2004

Results of Operations

Effective January 1, 2004, we realigned our organization based on the five target markets defined in on-top, our enterprise-wide strategy and structure project: Central Europe, Pan-European Gas, U.K., Nordic, and U.S. Midwest. To facilitate comparison, we provide pro forma figures for the prior year according to the new market unit structure; these pro forma figures do not affect the consolidated group figures. Strategy and Key Figures, a publication available at www.eon.com, contains more information about our market unit structure.

In addition, effective the same date, earnings before interest and taxes and adjusted for nonrecurring effects (“adjusted EBIT”) has replaced internal operating profit as our key performance measure (see commentary on pages 30-31).

We sold 4 percent more electricity in the first nine months of 2004 than in the same period last year. The increase is principally attributable to the inclusion of JME and JCE, regional distribution companies operating in the Czech Republic, and Graninge, a Swedish energy utility. On balance, we sold 2 percent more gas due to positive development at our Pan-European Gas market unit, particularly in the third quarter.

Consolidated Sales

Consolidated sales were higher, primarily because of the first-time inclusion of E.ON Ruhrgas and several European energy utilities for the entire period under review. E.ON Ruhrgas became a consolidated E.ON company on February 1, JME and JCE on October 1, and Graninge on November 1, 2003, and Midlands Electricity on January 16, 2004.

Adjusted EBIT

In the first three quarters of 2004, we grew adjusted EBIT by €885 million or 19 percent. All of our market units contributed to the increase. In particular, our international business posted marked earnings growth. The increase in adjusted

4

Interim Report III/2004

EBIT resulted from operating improvements and the inclusion of our successful acquisitions for the entire period under review. Furthermore, the results of our Central Europe market unit benefited from the reversal of provisions relating in part to the Renewable Energy Law and the Cogeneration Protection Law (for more information, see page 7).

Consolidated Net Income

Consolidated net income (after income taxes and minority interests) again surpassed the high prior-year figure, even though book gains were substantially lower, particularly those recorded under income from discontinued operations.

Adjusted interest income (net) improved in the first nine months of 2004 by €462 million, due primarily to a nonrecurring gain of approximately €270 million resulting from amendments to Germany’s Ordinance on Advance Payments for the Establishment of Federal Facilities for Safe Custody and Final Storage for Radioactive Wastes (Endlager-Vorausleistungsverordnung). Under the amended ordinance, construction costs for the final storage facilities at Gorleben and Konrad will now be shared fairly by nuclear plant operators and by other users, such as research institutes. Overall, this will lower our share of the costs, enabling us to reduce past provisions for nuclear waste management.

Net book gains in the period under review were below last year’s figure and resulted from the sale of equity interests in EWE and VNG (€317 million), the sale of securities (€152 million), and the sale of more Degussa stock (€63 million). The prior-year number consists of book gains on the sale of shares in Bouygues Telecom (€294 million) and Degussa (€168 million) and on the sale of securities at our Central Europe market unit (€152 million). The prior-year figure also includes book gains of roughly €80 million resulting from the sale of shareholdings at Central Europe and U.K. and a book loss of €76 million on the sale of HypoVereinsbank stock at Central Europe.

Restructuring expenses declined year-on-year to €40 million and in the period under review are primarily attributable to the integration of Midlands Electricity. In the same period a year ago, this item contained expenses relating to the creation of the regional utilities E.ON Hanse and E.ON Westfalen Weser and the integration of TXU activities.

Other nonoperating earnings were higher in the first three quarters of 2004, primarily reflecting positive effects from the marking to market of energy derivatives at the U.K. market unit. These derivatives are used to shield our operations from the effects of price volatility. Their value has increased by approximately €700 million since June 2004 on the back of sharply higher gas prices. The prior-year figure mainly includes the equity earnings from our RAG shareholding as well as positive effects from the marking to market of energy derivatives. Other nonoperating earnings were negatively affected in the prior-year period by the valuation adjustment taken at Degussa’s Fine Chemicals division.

The €713 million increase in our tax expense compared with the first nine months of 2003 stems in particular from improved operating results.

In the prior-year period, the cumulative effect of changes in accounting principles was primarily attributable to the adoption of the Statement of Financial Accounting Standards (SFAS) 143, Accounting for Asset Retirement Obligations.

5

Interim Report III/2004

Core Energy Business

Central Europe

Central Europe

Following a brief downward trend in spot and forward electricity prices in July 2004, prices on power exchanges in Central Europe rose markedly by the end of August. Key drivers were higher hard coal and oil prices. In September, a slight softening of European coal prices left forward prices stable at about €35 per MWh for baseload power.

Electricity prices for end-customers in Germany averaged roughly 3 percent higher year-on-year for standard rate service in the residential segment and approximately 10 percent higher for new contracts in the industrial segment. The increase in the industrial segment was driven by current wholesale price trends.

The Central Europe market unit sold 10.4 billion kWh more electricity than in the first nine months of last year, due mainly to the inclusion of JME and JCE, regional distribution companies operating in the Czech Republic, which together accounted for 9.2 billion kWh of the increase.

Central Europe met about 52 percent of its power requirements with electricity from its own generation assets, compared with 57 percent in the previous year. In its generation business, Central Europe is able to capitalize on the advantages of a balanced energy resource portfolio. From jointly owned power stations and outside sources, Central Europe procured around 15 billion kWh more electricity than in the first three quarters of last year. This increase is also principally attributable to the inclusion of JME and JCE and to decreased nuclear output following the shutdown of Stade nuclear power station late last year.

Gas sales volumes at Central Europe’s regional distribution companies were down 6 billion kWh from last year due to relatively milder temperatures.

6

Interim Report III/2004

Power Generation and Procurement¹

Central Europe grew sales by 8 percent relative to the year-earlier period, due mainly to the inclusion of JME and JCE for the entire period under review. Other positive factors were the recovery of electricity prices in Germany and slightly higher sales volumes.

Adjusted EBIT rose €447 million year-on-year. Central Europe’s business units showed the following development:

The Central Europe West Power business unit grew adjusted EBIT by €382 million or 20 percent. Approximately €140 million of the increase is attributable to the reversal of provisions resulting in part form a court decision expressly granting the right to pass on additional costs relating to the Renewable Energy Law and the Cogeneration Protection Law and from the reversal of provisions for refunds for allegedly excessive grid access fees. Prior-year results were negatively affected by balance area settlement payments. Absent these nonrecurring effects, adjusted EBIT would have risen roughly 7 percent in the period under review.

Gas Sales by Customer Segment¹

Positive factors contributing to this increase included the passthrough of higher wholesale electricity prices to ultimate customers and slightly higher sales volumes. A countervailing factor was higher expenditures for conventional fuel. The previous year’s market-driven increase in trading earnings was compensated for in the current year by further improvements in the conventional generating business and optimized cost management at our regional supply companies. A further driver was a reduction in costs for nuclear fuel and nuclear waste management. Earnings were negatively impacted by expenditures for obligations in electric transmission operations.

Adjusted EBIT at Central Europe West Gas was €14 million above the prior-year figure. The lower, weather-driven sales volume of the current-year period was counteracted by stable sales prices and optimized procurement management.

The Central Europe East business unit grew adjusted EBIT by €50 million, due principally to the inclusion of JME and JCE for the entire period under review.

Financial Highlights by Business Unit¹

7

Interim Report III/2004

Core Energy Business

Pan-European Gas

In the first nine months of 2004, Germany’s consumption of primary energy fell 0.6 percent, while its consumption of natural gas rose 1.3 percent, relative to the same period last year. Lower average temperatures in the third quarter led to a roughly 13 percent increase in natural gas consumption compared with the prior-year quarter.

The Pan-European Gas market unit sold 442.2 billion kWh of gas in the first three quarters of 2004, about 5 percent more than in the previous year. The positive volume growth of the second quarter of 2004 continued in the third quarter. On balance, third-quarter sales volume was up 29 percent year-on-year to 105.8 billion kWh, due mainly to higher sales to resellers along with a disproportional increase in the export business resulting from new contracts that were concluded with customers in Italy, France, and Denmark.

Pan-European Gas grew adjusted EBIT by 3 percent and sales by 16 percent in the first nine months of 2004. Current-year sales and adjusted EBIT include figures for January, which were not included in the previous year, since E.ON Ruhrgas became a consolidated E.ON company on February 1, 2003. Another factor leading to higher sales was the first-time inclusion of Thüga Italia’s operations at the Downstream Shareholdings business unit and E.ON Ruhrgas Norge in the Up-/Midstream business unit for the entire period under review.

Adjusted for the fact that last year’s figure did not include the month of January, sales at the midstream business were down year-on-year. The period under review was negatively impacted by lower temperature spikes compared with the prior year and by lower average sales prices. These factors were only partially offset by the overall positive development of sales volumes. The sales of Ruhrgas Industries, which are recorded at the Other/Consolidation business unit, were up slightly.

The adjusted EBIT performance of the midstream business was also burdened by the price- and weather-driven decline in sales. The current upward trend in oil prices negatively affected adjusted EBIT because there is a difference in the speed at which gas procurement prices and gas sales prices respond to oil price movements. The slight year-on-year increase in adjusted EBIT is likewise attributable to the inclusion of nine months in the current year against eight months in the prior year. The upstream business also benefited from the first-time inclusion of E.ON Ruhrgas Norge. In addition, the E&P business was aided by high oil prices.

Pan-European Gas

Gas Sales by Month¹

Adjusted EBIT of Downstream Shareholdings was down slightly, due in particular to a decline in equity earnings that is primarily related to the disposal of shareholdings. The impact of this development was diminished by proportionally higher equity earnings from SPP, a company operating in the Slovak Republic.

Prior-year results of Ruhrgas Industries, which are recorded under Other/Consolidation, were adversely affected by non-recurring charges stemming from the purchase price allocation. The absence of this one-off effect resulted in an improved adjusted EBIT performance.

Financial Highlights by Business Unit¹

8

Interim Report III/2004

U.K.

U.K.

Forward electricity prices have increased significantly during 2004, driven by higher fuel costs and environmental costs. Gas forward prices have risen dramatically compared with the prior year as a result of higher oil prices and the expectation that the United Kingdom will become a net importer of gas in the near future.

In response to higher wholesale energy prices, E.ON UK increased its residential retail prices during the period to September 30, 2004, by 6.9 percent for electricity and 8.2 percent for gas. On November 2, E.ON UK announced a further price increase of 8.9 percent for electricity and 9.6 percent for gas effective from November 29, 2004. A package of measures has been announced to help the more vulnerable customers. These price rises are in line with other U.K. energy suppliers.

The retail industrial and commercial (I&C) business was rebranded to E.ON Energy on July 5, 2004. The Powergen brand has been retained for the residential and small and medium enterprises (SME) business but will be phased out over a number of years. This follows the rebranding of the East Midlands and Midlands distribution businesses to Central Networks on April 5, 2004.

Sales by Customer Segment¹

The decrease in power and gas sales volumes reflects E.ON UK’s approach in the I&C market, where the focus has been on securing margin rather than volume.

Power Generation and Procurement

The decline in owned generation is explained by a reduction in margin on coal-fired plant due to higher wholesale coal prices and to the closure of Drakelow and High Marnham in 2003. Coal-fired power stations accounted for 62 percent of electricity generation during the current-year period.

9

Interim Report III/2004

Core Energy Business

The U.K. market unit’s attributable generation portfolio was 7,906 MW at September 30, 2004, a decrease of 1,708 MW from year end 2003 due to the mothballing of plant at Grain and Killingholme.

E.ON UK increased its sales in 2004 compared with the prior year as a result of the first-time consolidation of the Midlands Electricity business, retail price increases, and positive exchange-rate effects, partially offset by lower retail volumes. Adjusted EBIT of €720 million was recorded up to September 30, 2004, of which €321 million was in the regulated business and €433 million in the non-regulated business.

The consolidation of the Midlands Electricity business acquired in January 2004 is the main reason for the €154 million increase in adjusted EBIT from the regulated business.

The €72 million increase in adjusted EBIT for the non-regulated business is mainly due to higher retail earnings offset by higher coal and gas costs and the continued savings from the integration of the TXU business acquired in 2002.

Financial Highlights by Business Unit¹

Nordic

Nordic

Up to mid-August, water supply conditions in Sweden and Norway remained more than 20 billion kWh below average hydro. With coal prices extremely high, spot electricity prices remained at high levels, and forward prices increased considerably. Following heavy rainfall during the early autumn, water supply conditions improved to nearly average hydro. Although coal prices have remained high, spot and forward electricity prices have declined significantly.

10

Interim Report III/2004

The Nordic market unit increased electricity sales by 6.7 billion kWh compared with the corresponding period in 2003. Sales to residential and business customers were up 3.1 billion kWh, due mainly to the inclusion of Graninge. Sales to minority partners and Nordpool rose owing to higher hydroelectric and nuclear generation in existing operations.

Two thirds of Nordic’s electricity sales were generated at its own assets. The Graninge acquisition was responsible for 2.7 billion kWh of the increase in owned generation, with higher output at existing operations accounting for 2.3 billion kWh. Nuclear power production increased as a consequence of very high availability during the current year. Improved water supply conditions resulted in higher hydroelectric output. During the first nine months of 2004, Nordic’s nuclear power plants produced 54 percent of total generation, while hydroelectric plants accounted for 39 percent.

Gas sales and heat sales increased by 0.2 billion kWh and 0.5 billion kWh, respectively, compared with the first nine months of 2003, due mainly to the inclusion of Graninge.

Nordic increased sales by €353 million in the first nine months of 2004 and grew adjusted EBIT by €138 million to €489 million. €58 million of the increase is attributable to the consolidation of Graninge. The remainder is a result of higher nuclear and hydroelectric output and better margins in the retail electricity business.

Power Generation and Procurement

Gas and Heat Sales

11

Interim Report III/2004

Core Energy Business

U.S. Midwest

U.S. Midwest

Wholesale electricity prices in the Midwest, driven in part by higher gas prices, increased to approximately $43 per MWh in the third quarter, compared with $38 per MWh for the same period in 2003. Damage from Hurricane Ivan continued to reduce Gulf of Mexico gas production, but the lack of weather-related demand allowed rising U.S. storage levels to exceed the five-year average by the end of the quarter.

Sales by Customer Segment

Through September 30, 2004, the regulated utility operation sold more electricity compared with 2003 due to increases in retail electric customer sales as a result of warm spring weather. Natural gas sales declined due largely to mild winter weather conditions in 2004.

The non-regulated operation showed higher electricity sales as a result of warm spring weather in 2004 and improved plant performance.

Power Generation and Procurement

Ninety-nine percent of the U.S. Midwest market unit’s electricity generation was from coal-fired power stations. At September 30, 2004, U.S. Midwest’s generation portfolio grew by 590 MW from year end 2003 to 9,663 MW due largely to the addition of four gas-fired combustion turbines.

U.S. Midwest’s sales for the first three quarters of 2004 decreased 3 percent to €1,436 million, resulting from the deterioration of the U.S. dollar against the euro. In local currency, however, sales improved by 6 percent, led by higher retail sales in utility operations. Adjusted EBIT increased 12 percent in reporting currency and 23 percent in local currency.

Adjusted EBIT at LG&E Energy’s regulated utility operations improved from 2003, primarily as a result of higher retail sales and the increased retail electric and gas rates approved by the Kentucky Public Service Commission. In addition, the contribution from off-system sales exceeded the previous year due to higher prices in the off-system wholesale electric market. These local currency increases in sales were partially offset by adverse exchange-rate movements as the U.S. dollar weakened against the euro. Increased sales also more than offset the impact of severe spring and summer storms, which caused significant damage to the utility operation’s distribution network.

Adjusted EBIT at LG&E Energy’s non-regulated operations was relatively consistent with 2003. U.S. Midwest’s Western Kentucky Energy operation improved due to enhanced plant performance. This was offset by the impact of the peso’s deterioration against the U.S. dollar for the Argentine operation.

Financial Highlights by Business Unit

12

Interim Report III/2004

Corporate Center

The Corporate Center consists of equity interests managed directly by E.ON AG, E.ON AG itself, and consolidation effects at the group level.

Corporate Center

Other Activities

Other activities consist of our Viterra and Degussa shareholdings. Effective February 1, 2003, Degussa has been accounted for using the equity method. From this date to May 31, 2004, this reflected E.ON’s 46.5 percent shareholding in the company. Under the equity method, Degussa’s sales are not included in E.ON’s consolidated sales, and a proportional share of Degussa’s earnings after taxes and minority interests are recorded in E.ON’s consolidated earnings. After selling more Degussa stock, E.ON owns 42.9 percent of Degussa effective June 1, 2004. Degussa contributed €113 million to adjusted EBIT in the first three quarters of 2004, compared with €148 million in the same period a year ago.

Viterra

Viterra performed well in the period under review, further increasing the number of housing units sold. Viterra sold 7,544 housing units, approximately 20 percent more than the prior-year figure of 6,294 units. The increase results in particular from the sale of a block of multifamily homes in the Ruhr region containing roughly 2,700 units.

Viterra’s sales were down €78 million relative to the same period last year. The main reasons were a decline in rental revenues in the wake of housing unit sales in the residential real estate business, lower sales in apartment buildings at Viterra Development, and the absence of revenue streams from Viterra Baupartner, which was phased out in late 2003.

Viterra’s adjusted EBIT was nearly at the prior-year level. In the residential real estate business, adjusted EBIT was up about 8 percent, in particular due to the increase in the number of housing units sold and to operational improvements. By contrast, adjusted EBIT at Viterra Development declined owing primarily to lower earnings in apartment building construction and a reduction in earnings streams from logistics facilities caused in particular by the absence of earnings on rental revenues from the Rudná Logistics Park near Prague which was sold in late 2003.

13

Interim Report III/2004

Employees

Employees¹

At the end of September 2004, the E.ON Group had 69,380 employees worldwide, as well as 2,472 apprentices and 284 board members and managing directors. As of this date, 32,890 employees, 47 percent of all staff, were working outside Germany. E.ON’s workforce has increased by 2,278 employees since year end 2003. This development is mainly attributable to the U.K. market unit’s acquisition of Midlands Electricity in the first quarter of 2004, which increased the group’s staff count by 3,700 employees.

By contrast, the Nordic market unit’s workforce declined by 679 employees from the figure for year end 2003, due mainly to the disposal of two service subsidiaries in Sweden and the termination of seasonal employment contacts.

The reduction in staff count at Viterra is attributable to the phase-out of Viterra Baupartner and to other restructuring measures.

During the reporting period, wages and salaries including social security contributions totaled €3.4 billion, compared with €3.6 billion a year ago; the latter figure includes €259 million for Degussa for January 2003.

Investments

Investments by Market Unit

In the period under review, the E.ON Group’s capital expenditures declined by €3.5 billion, or 48 percent, from the prior-year figure, which included the acquisition of Ruhrgas shares recorded under Corporate Center. E.ON invested €1.7 billion in intangible assets and property, plant, and equipment, roughly the same amount as in the first nine months of 2003. Investments in financial assets totaled €2.1 billion, versus €5.6 billion in the prior year.

The Central Europe market unit invested 12 percent more than in the previous year. Capital expenditures for property, plant, and equipment totaled €773 million, compared with €761 million a year ago; financial investments totaled €711 million, compared with €563 million in the year-earlier span. The greater part of capital expenditures for property, plant, and equipment went toward power generation and distribution assets. Financial investments predominantly reflect the acquisition of shareholdings from the Pan-European Gas market unit as part of the group-wide program to optimize E.ON’s shareholding structure.

E.ON UK’s capital expenditure in the period to September 30, 2004, was €375 million, €109 million more than in the first nine months of 2003. The increase is mainly due to expenditure in the newly acquired Midlands Electricity business. Investments in property, plant, and equipment focused on the expansion of the renewable generation portfolio and the upgrade of the distribution network as well as on the maintenance of conventional power stations.

14

Interim Report III/2004

During the first nine months of 2004, the Nordic market unit invested €245 million in property, plant, and equipment in order to maintain its existing production plants and to upgrade and enhance its distribution network. Investments in financial assets totaling €376 million were directed mainly toward the acquisition of additional Graninge shares, giving E.ON Nordic 100 percent ownership of the company.

E.ON Stock

The value of E.ON stock (including the dividend) rose 18 percent in the first nine months of 2004, significantly outperforming other European blue chips as measured by the EURO STOXX 50 Performance Index, which advanced 2 percent over the same period. E.ON stock performance was slightly under that of its peer index, the STOXX Utilities, which finished September 2004 20 percent higher than its year-end 2003 closing. The trading volume of E.ON stock climbed by 12 percent year-on-year to €33.0 billion, making E.ON the seventh most-traded stock in the DAX index of Germany’s top 30 blue chips. As of September 30, 2004, E.ON was the third-largest DAX issue in terms of market capitalization.

For the latest information about E.ON stock, visit www.eon.com.

E.ON Stock

High, Low, and Trading Volume