The information in this prospectus supplement is not complete and may be changed. This prospectus supplement and the accompanying prospectus relate to an effective registration statement filed with the Securities and Exchange Commission and are not an offer to sell these securities and are not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Filed pursuant to Rule 424(b)(5)

17,000,000 Shares

Common Stock

        We are selling up to 17,000,000 shares of common stock of Capstone Turbine Corporation offered by this prospectus supplement.

      Our common stock is listed on the Nasdaq National Market under the symbol “CPST.” On October 6, 2005, the last reported sale price of our common stock on the Nasdaq National Market was $3.29 per share.

       Investing in our common stock involves risks — see “Risk Factors” on page S-3 of this prospectus supplement.

       The price to public, related fees and proceeds to us are not determinable at this time. The price per share will be based on a 4% discount from the volume weighted average price on the Nasdaq National Market for each day during the ten (10) trading days commencing on October 10, 2005. We estimate the expenses of the offering to be approximately $2,000,000, including related advisory fees equal to 3.5% of the aggregate offering price. See “Plan of Distribution.”

      Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the prospectus to which it relates is truthful or complete. Any representation to the contrary is a criminal offense.

      Delivery of the shares of common stock will be made on various dates between October 10, 2005 and October 24, 2005, unless extended. Certain purchaser funds will be deposited into an escrow account and held until the dates of release to the purchaser.

The date of this prospectus supplement is October 7, 2005.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

      You should rely only on the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. We have not authorized any other person to provide you with any information that is different. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. The information contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference is accurate only as of their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates.

      The information contained in this prospectus supplement and accompanying prospectus is being supplied in the United Kingdom only to persons with professional experience in matters relating to investments and/or to high net worth companies as described in Articles 19(5) and 49(2) respectively of the United Kingdom Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (as amended) made pursuant to Section 21(5) of the United Kingdom Financial Services and Markets Act 2000 (the “Financial Promotion Order”). The information contained in this prospectus supplement and accompanying prospectus are not intended to be viewed by, or distributed or passed on (directly or indirectly) to, any other class of persons in the United Kingdom.

      In purchasing or agreeing to purchase any of our common stock offered by this prospectus supplement, any purchaser who is resident in the United Kingdom confirms that they are either a person with professional experience in matters relating to investments or a high net worth company as described in Articles 19(5) and 49(2) respectively of the Financial Promotion Order.

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ABOUT THIS PROSPECTUS SUPPLEMENT

      This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. We are providing information to you about this offering in two separate documents that are combined together. The first document is the prospectus supplement, which provides you with the specific details regarding this offering, including the price, the amount of common stock being offered and the risks of investing in our common stock. The second document is the accompanying prospectus, which provides you with more general information, some of which may not apply to this offering. Generally, when we refer to the prospectus, we are referring to both documents combined. If information in this prospectus supplement is inconsistent with the accompanying prospectus or any of the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, you should rely on this prospectus supplement. You should read both this prospectus supplement and the accompanying prospectus together with the additional information described under the heading “Where You Can Find More Information.”

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S-2

RISK FACTORS

      Investing in our common stock involves a high degree of risk. You should consider carefully each of the following risks and all other information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus before deciding to purchase shares of our common stock. If any of the risks described below actually occur, our business, financial condition and operating results could be adversely affected. As a result, the trading price of our common stock could decline, perhaps significantly, and you could lose all or part of your investment.

Risks Related to Our Business and Operations

      Since inception, we have incurred annual operating losses. We expect to become profitable by the end of Fiscal 2007. To become profitable, we must sell a sufficient number of units and achieve a lower cost structure. Our business is such that we have had relatively few customers and limited repeat business. As a result, we may not maintain or increase net revenues. We may not have adequate cash resources to reach the point of profitability, and we may never become profitable. Even if we do achieve profitability, we may be unable to increase our sales, and sustain or increase our profitability in the future.

      Our products represent an emerging market, and we do not know whether our targeted customers will accept our technology or will purchase our products in sufficient quantities to allow our business to grow. To succeed, demand for our products must increase significantly in existing markets and there must be strong demand for products that we introduce in the future. If a sustainable market fails to develop or develops more slowly than we anticipate, we may be unable to recover the losses we have incurred to develop our products, we may have further impairment of assets, and we may be unable to meet our operational expenses. The development of a sustainable market for our systems may be hindered by many factors, including some that are out of our control. Examples include:

	•	consumer reluctance to try a new product;
	•	regulatory requirements;
	•	the cost competitiveness of our microturbines;
	•	costs associated with the installation and commissioning of our microturbines;
	•	maintenance and repair costs associated with our microturbines;
	•	the future costs and availability of fuels used by our microturbines;
	•	economic downturns and reduction in capital spending;
	•	consumer perceptions of our microturbines’ safety and quality;
	•	the emergence of newer, more competitive technologies and products; and
	•	decrease in domestic and international incentives.

      Capstone MicroTurbines compete with several technologies, including reciprocating engines, fuel cells and solar power. Competing technologies may receive certain benefits, like governmental subsidies or promotion, or consumer rebates or other incentives that we do not enjoy or do not benefit from to the

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      Our competitors include several well-known companies with histories of providing power solutions. They have substantially greater resources than we have and have established worldwide presence. Because of greater resources, some of our competitors may be able to adapt more quickly to new or emerging technologies and changes in customer requirements, to devote greater resources to the promotion and sale of their products than we can or they may introduce governmental regulations and policies to create competitive advantage vis-à-vis our products. We believe that developing and maintaining a competitive advantage will require continued investment by us in product development and quality, as well as attention to product performance, our product prices, our conformance to industry standards, manufacturing capability and sales and marketing. In addition, current and potential competitors have established, or may in the future establish, collaborative relationships among themselves or with third parties, including third parties with whom we have business relationships. Accordingly, new competitors or alliances may emerge and rapidly acquire significant market share.

      Overall, the market for our products is highly competitive and is changing rapidly. We believe that the primary competitive factors affecting the market for our products, including some that are outside of our control, include:

	•	name recognition, historical performance and market power of our competitors;
	•	product quality and performance;
	•	operating efficiency;
	•	product price;
	•	availability and price of fuel;
	•	development of new products and features; and
	•	emissions levels.

      There is no assurance that we will be able to successfully compete against either current or potential competitors, or that competition will not have a material adverse effect on our business, operating results and financial condition.

      Our sales and marketing efforts may not achieve intended results and therefore may not generate the net revenues we anticipate. As a result of our strategic plan, we have decided to focus our resources on selected vertical markets, such as secure power, cogeneration (CHP and CCHP), and resource recovery. We may change our focus to other markets or applications in the future. There can be no assurance that our focus or our near term plans will be successful. If we are not able to successfully address markets for our products, we may not be able to grow our business, compete effectively or achieve profitability.

      As a result of our strategic planning process, we have begun offering direct sales and service in selected markets. We do not have extensive experience in providing direct sales and service and may not be successful in executing this strategy. In addition, we may lose existing distributors or service providers or we may have more difficulty attracting new distributors and service providers as a result of this strategy. Further we may incur new types of obligations, such as extended service obligations, that could result in costs that exceed the related revenues. We may encounter new transaction types through providing direct sales and service and these transactions may require changes to our historic business practices. For example, an arrangement with a third party leasing company may require us to provide a residual value guarantee, which is not consistent with our past operating practice.

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      Also, as we expand in international markets, customers may have difficulty or be unable to integrate our products into their existing systems or may have difficulty complying with foreign regulatory and commercial requirements. As a result, our products may require redesign. Any redesign of the product may delay sales or cause quality issues. In addition, we may be subject to a variety of other risks associated with international business, including import/export restrictions, fluctuations in currency exchange rates and global political and economic instability.

      In order to serve certain of our targeted markets, we believe that we must ally ourselves with companies that have particular expertise or better access to those markets. We believe that retaining or developing strong distributors in these targeted markets can improve the rate of adoption as well as reduce the direct financial burden of introducing a new technology and creating a new market. Because of distributors’ relationships in their respective markets, the loss of a distributor could adversely impact the ability to penetrate its target market. At the present time, we offer our distributors a stated discount from list price for the products they purchase. In the future, to attract and retain distributors, we may provide volume price discounts or otherwise incur significant costs that may reduce the potential profitability of these relationships. We may not be able to retain or develop appropriate distributors on a timely basis, and we cannot assure you that the distributors will focus adequate resources on selling our products or will be successful in selling them. In addition, some of the relationships may require that we grant exclusive distribution rights in defined territories. These exclusive distribution arrangements could result in our being unable to enter into other arrangements at a time when the distributor with whom we form a relationship is not successful in selling our products or has reduced its commitment to market our products. We cannot assure you that we will be able to negotiate collaborative relationships on favorable terms or at all. The inability of the Company to have appropriate distribution in our target markets may adversely affect our financial condition and results of operations.

      Sales to United Technologies Corporation (“UTC”) accounted for approximately 15% of the Company’s net revenues for Fiscal 2005 and 40% of the Company’s net revenues for the quarter ended June 30, 2005. Over the past year, UTC’s performance as it relates to engineering, installation and provision of aftermarket services has been inadequate, and, if not rectified, could have a significant impact on our reputation and products. On September 11, 2005, we gave notice pursuant to our OEM agreement with UTCP, an affiliate of UTC, of certain breaches of the OEM agreement by UTCP, including failure to meet sales targets for the year. With respect to most of the breaches, UTCP will have ninety (90) calendar days following its receipt of the notice in which to cure the breaches or the OEM agreement will terminate. The OEM agreement permits UTCP to package the Company’s MicroTurbine products with chillers and heat exchange equipment manufactured by UTCP and to sell and service the integrated combined cooling heat and power generation units. If this relationship is terminated, our near-term sales, cash flow and profitability could be adversely affected. Furthermore, while this relationship is important to us, UTC has not and may not achieve its forecasted sales growth, which could affect our ability to meet our sales, cash flow and profitability targets. See “Capstone Turbine Corporation — Recent Developments.”

      Our ability to identify and develop business relationships with companies who can provide quality, cost-effective application engineering, installations and service can significantly affect our success. The application engineering and proper installation of our microturbines, as well as proper maintenance and service, are critical to the performance of the units. Additionally, we need to reduce the total installed cost

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      We have entered into agreements with some of our distributors and ASCs. These agreements require that if we render parts obsolete in inventories they own and hold in support of their obligations to serve fielded microturbines, then we are required to replace the affected stock at no cost to the distributors or ASCs. While we have never incurred costs or obligations for these types of replacements, it is possible that future changes in our product technology could result and yield costs that have a material adverse effect on our results of operations or financial position.

      Our products are subject to federal, state, local and foreign laws and regulations, governing, among other things, emissions to air and occupational health and safety. Regulatory agencies may impose special requirements for implementation and operation of our products (e.g., connection with the electric grid) or may significantly affect or even eliminate some of our target markets. We may incur material costs or liabilities in complying with government regulations. In addition, potentially significant expenditures could be required in order to comply with evolving environmental and health and safety laws, regulations and requirements that may be adopted or imposed in the future. For example, our current products do not comply with the 2007 proposed emission standards of the California Air Resources Board. Furthermore, our potential utility customers must comply with numerous laws and regulations. The deregulation of the utility industry may also create challenges for our marketing efforts. For example, as part of electric utility deregulation, federal, state and local governmental authorities may impose transitional charges or exit fees, which would make it less economical for some potential customers to switch to our products. We can provide no assurances that we will be able to obtain these approvals and changes in a timely manner, or at all.

      The market for electricity and generation products is heavily influenced by federal and state government regulations and policies. The deregulation and restructuring of the electric industry in the United States and elsewhere may aid the desirability of alternative power sources. Problems associated with such deregulation and restructuring may cause rule changes that may reduce or eliminate advantages of such deregulation and restructuring. We cannot predict how the deregulation and the restructuring of the electric utility industry will ultimately affect the market for our microturbines. Changes in regulatory standards or policies could reduce the level of investment in the research and development of alternative power sources, including microturbines. Any reduction or termination of such programs can increase the cost to our potential customers, making our systems less desirable, and thereby adversely affect our revenue and potential profitability.

      Utility companies or governmental entities could place barriers on the installation of our product or the interconnection of the product with the electric grid. Further, they may charge additional fees to customers who install on-site generation, or for having the capacity to use power from the grid for back-up or standby purposes. These types of restrictions, fees or charges could hamper the ability to install or effectively use our product or increase the cost to our potential customers for using our systems. This could make our systems less desirable, thereby adversely affecting our revenue and profitability potential. In addition, utility rate reductions can make our products less competitive which would have a material adverse effect on our operations. The cost of electric power generation is ultimately tied to the cost of natural gas. However, changes to utility electric tariffs often require lengthy regulatory approval, and

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      As we continue to improve the quality and lower the total costs of ownership of our products, we may require engineering changes. Such improvement initiatives may render existing inventories obsolete or excessive. Despite our continuous quality improvement initiatives, we may not meet customer expectations. Any significant quality issues with our products could have a material adverse effect on our rate of product adoption, results of operations and financial position. Moreover, as we develop new configurations for our microturbines or as our customers place existing configurations in commercial use, our products may perform below expectations. Any significant performance below expectations could adversely affect our operating results and financial position and affect the marketability of our products.

      We sell our products with warranties. While management believes that the provision for estimated product warranty expenses is reasonable, there can be no assurance that the provision will be sufficient to cover our warranty expenses in the future. Although we attempt to reduce our risk of warranty claims through warranty disclaimers, we cannot ensure that our efforts will effectively limit our liability. Any significant incurrence of warranty expense in excess of estimates could have a material adverse effect on our operating results and financial position. Further, we have at times undertaken programs to enhance the performance of units previously sold. These enhancements have at times been provided at no cost or below our cost. While we believe we have no obligations to offer such programs, we may choose to do so again in the future and such actions could result in significant costs.

      Our operating results may depend on our ability to develop and introduce new products, or enhance existing products and to reduce the costs to produce our products. The success of our products is dependent on several factors, including proper product definition, product cost, timely completion and introduction of the products, differentiation of products from those of our competitors, meeting changing customer requirements, emerging industry standards and market acceptance of these products. The development of new, technologically advanced products and enhancements is a complex and uncertain process requiring high levels of innovation, as well as the accurate anticipation of technological and market trends. There can be no assurance that we will successfully identify new product opportunities, develop and bring new or enhanced products to market in a timely manner, successfully lower costs and achieve market acceptance of our products, or that products and technologies developed by others will not render our products or technologies obsolete or noncompetitive.

      As a result of our strategic plan, we have identified opportunities to outsource to third party suppliers certain functions which we currently perform. We believe outsourcing can reduce product costs, improve product quality or increase operating efficiency. These actions may not yield the expected results, and outsourcing may result in delay or lower quality products. Transitioning to outsourcing may cause certain affected employees to leave the company before the outsourcing is complete. This could result in a lack of the experienced in-house talent necessary to successfully implement the outsourcing. Further, depending on the nature of operations outsourced and the structure of agreements we reach with suppliers to perform these functions, we may experience impairment in the value of manufacturing assets related to the outsourced functions or other unanticipated charges, which could have a material adverse effect on our operating results.

S-7

      We believe that we will need to reduce the unit production cost of our products over time to maintain our ability to offer competitively priced products. Our ability to achieve cost reductions will depend on our ability to develop low cost design enhancements, to obtain necessary tooling and favorable supplier contracts and to increase sales volumes so we can achieve economies of scale. We cannot assure you that we will be able to achieve any such production cost reductions. Our failure to achieve such cost reductions could have a material adverse effect on our business and results of operations.

      Our products contain a number of commodity materials, from metals, which includes steel, special high temperature alloys, copper, nickel and molybdenum, to computer components. The availability of these commodities could impact our ability to acquire the materials necessary to meet our requirements. The cost of metals has historically fluctuated. The pricing could impact the costs to manufacture our product. If we are not able to acquire commodity materials at prices and on terms satisfactory to us or at all, our operating results may be materially adversely affected.

      Although we generally attempt to use standard parts and components for our products, some of our components are currently available only from a single source or limited sources. We may experience delays in production if we fail to identify alternative suppliers, or if any parts supply is interrupted, each of which could materially adversely affect our business and operations. In order to reduce manufacturing lead times and ensure adequate component supply, we enter into agreements with certain suppliers that allow them to procure inventory based upon criteria defined by us. If we fail to anticipate customer demand properly, an oversupply of parts could result in excess or obsolete inventories, which could adversely affect our business. Our inability to meet volume commitments with suppliers could affect the availability or pricing of our parts and components. A reduction or interruption in supply, a significant increase in price of one or more components or a decrease in demand of products could materially adversely affect our business and operations and could materially damage our customer relationships. Financial problems of suppliers on whom we rely could limit our supply or increase our costs. Also, we cannot guarantee that any of the parts or components that we purchase will be of adequate quality or that the prices we pay for the parts or components will not increase. Inadequate quality of products from suppliers could interrupt our ability to supply quality products to our customers in a timely manner. Additionally, defects in materials or products supplied by our suppliers that are not identified before our products are placed in service by our customers could result in higher warranty costs and damage to our reputation. We also outsource approximately 2% of our components internationally and expect to increase to approximately 20% by the first quarter of Fiscal 2007. As a result of outsourcing internationally, we may be subject to delays in delivery due to import/ export, delays in transportation or regional instability.

      The sale of our products typically involves a significant commitment of capital by customers, with the attendant delays frequently associated with large capital expenditures. For these and other reasons, the sales cycle associated with our products is typically lengthy and subject to a number of significant risks over which we have little or no control. We expect to plan our production and inventory levels based on internal forecasts of customer demand, which is highly unpredictable and can fluctuate substantially. If sales in any period fall significantly below anticipated levels, our financial condition and results of operations could suffer. If demand in any period increases well above anticipated levels, we may have difficulties in responding, incur greater costs to respond, or be unable to fulfill the demand in sufficient time to retain the order, which would negatively impact our operations. In addition, our operating expenses

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      We may face litigation relating to intellectual property matters, labor matters, product liability, or other matters. An adverse judgment could negatively impact our financial position and results of operations, the price of our common stock and our ability to obtain future financing on favorable terms or at all. Any litigation could be costly, divert management attention or result in increased costs of doing business.

      To the extent that the funds on hand are insufficient to fund our future operating requirements, we would need to raise additional funds, through further public or private equity or debt financings depending upon prevailing market conditions. These financings may not be available or, if available, may be on terms that are not favorable to us and could result in dilution to our stockholders. Downturns in worldwide capital markets could also impede our ability to raise additional capital on favorable terms or at all. If adequate capital were not available to us, we would likely be required to significantly curtail or possibly even cease our operations.

      If we are successful in executing our business plan, we will experience growth in our business that could place a significant strain on our business operations, management and other resources. Our ability to manage our growth will require us to expand our production capabilities, continue to improve our operational, financial and management information systems, and to motivate and effectively manage our employees. We cannot assure you that our systems, procedures and controls or financial resources will be adequate, or that our management will keep pace with this growth. We cannot assure you that our management will be able to manage this growth effectively.

      Our success depends in significant part upon the continuing service of our executive officers, senior management, including our chief executive officer, John Tucker, and sales and technical personnel. The failure of our personnel to execute our strategy, or our failure to retain management and personnel, could have a material adverse effect on our business. Our success will be dependent on our continued ability to attract, retain and motivate highly skilled employees. There can be no assurance that we can do so.

      Our internal control systems rely on people trained in the execution of the controls. Loss of these people or our inability to replace them with similarly skilled and trained individuals or new processes in a timely manner could further adversely impact our internal control mechanisms.

      Pursuant to Section 404 of the Sarbanes-Oxley Act of 2002, we are required to include in our Annual Report on Form 10-K our assessment of the effectiveness of our internal controls over financial reporting. Furthermore, our independent registered public accounting firm is required to audit our assessment of the effectiveness of our internal controls over financial reporting and separately report on whether it believes we maintain, in all material respects, effective internal controls over financial reporting. We identified three material weaknesses in our system of internal controls as of March 31, 2005. The first related to setting up

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      Since March 31, 2005, we believe we have adequately addressed the first and second material weaknesses, however, we have continued to identify a material weakness related to the effectiveness of internal controls over inventory as it relates to custody and control of assets. The deficiencies were concluded to be a material weakness based on the significance of the controls over inventory to the preparation of reliable financial statements. We cannot assure you that our system of internal controls will be effective in the future as our operations and control environment change. If we cannot adequately maintain the effectiveness of our internal controls over financial reporting, our financial reporting may be inaccurate. If reporting errors actually occur, we could be subject to sanctions or investigation by regulatory authorities, such as the Securities and Exchange Commission. These results could adversely affect our financial results or the market price of our common stock.

      Our operations are vulnerable to interruption by fire, earthquake and other events beyond our control. Our executive offices and manufacturing facilities are located in Southern California. Because the Southern California area is located in an earthquake-sensitive area, we are particularly susceptible to the risk of damage to, or total destruction of, our facilities in Southern California and the surrounding transportation infrastructure, which could affect our ability to make and transport our products. While the Company does maintain personal property and business interruption coverage, it does not maintain earthquake coverage for personal property or resulting business interruption. If an earthquake, fire or other natural disaster occurs at or near our facilities, our business, financial condition and operating results could be materially adversely affected.

      An investment in our common stock is risky, and you could suffer significant losses and wide fluctuations in the market value of your investment. The market price of our common stock is highly volatile and is likely to continue to be volatile. As a result of the factors discussed below, our operating results for a particular quarter are difficult to predict. Given the continued uncertainty surrounding many variables that may affect the industry in which we operate, our ability to foresee results for future periods is limited. This variability could affect our operating results and thereby adversely affect our stock price. Many factors that contribute to this volatility are beyond our control and may cause the market price of our common stock to change, regardless of our operating performance. Factors that could cause fluctuation in our stock price may include, among other things:

	•	actual or anticipated variations in quarterly operating results;
	•	market sentiment toward alternate energy stocks in general or toward Capstone;
	•	changes in financial estimates or recommendations by securities analysts;
	•	conditions or trends in our industry or the overall economy;
	•	loss of one or more of our significant customers;
	•	errors, omissions or failures by third parties in meeting commitments to the Company;
	•	changes in the market valuations or earnings of our competitors or other technology companies;
	•	the trading of options on our common stock;
	•	announcements by us or our competitors of significant acquisitions, strategic partnerships, divestitures, joint ventures or other strategic initiatives;

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	•	announcements of significant market events, such as power outages, regulatory changes or technology changes;
	•	changes in the estimation of the future size and growth rate of our market;
	•	capital commitments;
	•	additions or departures of key personnel;
	•	sales or purchases of the company’s common stock;
	•	the trading volume of our common stock;
	•	developments relating to litigation or governmental investigations; and
	•	decrease in oil prices.

      In addition, the stock market in general, and the Nasdaq National Market and the market for technology companies in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of particular companies affected. The market prices of securities of technology companies and companies servicing the technology industries have been particularly volatile. These broad market and industry factors may cause a material decline in the market price of our common stock, regardless of our operating performance. In the past, following periods of volatility in the market price of a company’s securities, securities class-action litigation has often been instituted against that company. This type of litigation, if instituted against us and regardless of whether we prevail on the underlying claim, could result in substantial costs and a diversion of management’s attention and resources, which could materially harm our financial condition and results of operations.

      Sales of a substantial number of our shares of common stock in the public market following this offering, or the perception that these sales could occur, could substantially decrease the market price of our common stock. All the shares sold in this offering will be freely tradeable without restriction or further registration under federal securities laws, other than those shares sold to our affiliates. We cannot predict the effect, if any, that future sales of common stock, or the availability of common stock for future sale, will have on the market price of our common stock prevailing from time to time. We may also sell additional shares of common stock in subsequent public offerings, which may adversely affect market prices for our common stock.

      We do not plan to pay dividends on our common stock in the foreseeable future. The payment of future cash dividends, if any, will be at the discretion of our board of directors and will depend upon, among other things, conditions then existing, including our earnings, financial condition and capital requirements, restrictions in financing agreements, business opportunities and conditions, and other factors. Consequently, your only opportunity to achieve a return on your investment in our common stock, will be if the market price of our common stock appreciates and you sell your shares at a profit.

      Provisions of our second amended and restated certificate of incorporation, amended and restated bylaws and our stockholder rights plan, as well as provisions of the General Corporation Law of the State of Delaware, could discourage, delay or prevent unsolicited proposals to merge with or acquire us, even though such proposals may be at a premium price or otherwise beneficial to you. These provisions include

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      We are subject to the provisions of Section 203 of the General Corporation Law of the State of Delaware, which could prevent us from engaging in a business combination with a 15% or greater stockholder for a period of three years from the date it acquired such status unless appropriate board or stockholder approvals are obtained.

      Our board of directors has adopted a stockholder rights plan, pursuant to which one preferred stock purchase right has been issued for each share of our common stock authorized and outstanding at the close of business on July 18, 2005. The rights plan is intended to protect our stockholders in the event of an unfair or coercive offer to acquire the Company. However, the existence of the rights plan may discourage, delay or prevent a merger or acquisition of the Company that is not supported by the board of directors.

      We anticipate using the net proceeds of this offering for general corporate purposes. Our management will have considerable discretion in the application of these net proceeds, and you will not have the opportunity to assess whether the proceeds are being used appropriately. The net proceeds from this offering may be used for corporate purposes that do not increase our operating results or market value, and until they are used, they may be placed in investments that do not produce income or that lose value.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

      This prospectus supplement (including the information incorporated by reference) contains “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”) and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Forward-looking statements include statements concerning, among other things, our future results of operations, research and development activities, sales expectations, our ability to develop markets for our products, sources for parts, federal, state and local regulations, and general business, industry and economic conditions applicable to us. When used in this prospectus supplement, the words “estimates,” “expects,” “anticipates,” “projects,” “plans,” “intends,” “believes,” “should,” “could,” “may” and variations of such words or similar expressions are intended to identify forward-looking statements. All forward-looking statements, including, without limitation, our examination of historical operation trends, are based upon our current expectations and various assumptions.

      There are a number of risks and uncertainties that could cause our actual results to differ materially from the forward-looking statements contained in this prospectus supplement, including those risks described above. We caution you that these factors, as well as the risk factors included or incorporated by reference in this prospectus supplement, may not be exhaustive. Our actual results, performance or achievements could differ materially from the results expressed in, or implied by, these forward-looking statements. We operate in a continually changing business environment, and new risk factors emerge from time to time. We cannot accurately predict such future risk factors, nor can we assess the impact, if any, of such possible future risk factors on our businesses or the extent to which any factor or combination of factors may cause actual results to differ materially from those expressed or implied by any forward-looking statements. You are advised to review any further disclosures we make on related subjects in reports we file with the SEC. All forward-looking statements attributable to us or persons acting on our behalf apply only as of the date of this prospectus supplement and are expressly qualified in their entirety by the cautionary statements included in this prospectus supplement. We undertake no obligation to publicly update or revise forward-looking statements, which may be made to reflect events or circumstances after the date made or to reflect the occurrence of unanticipated events, except as required by applicable securities laws.

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USE OF PROCEEDS

      We expect to receive net proceeds from the sale of our common stock in this offering of approximately $52 million after deducting the estimated offering expenses payable by us and assuming (i) all of the shares offered hereby are purchased and (ii) the offering price of $3.27 per share, the initial price at which shares are purchased in the offering.

      We intend to use the net proceeds from shares sold by us in the offering for general corporate purposes, which may include, but are not limited to, working capital, capital expenditures and repurchases or redemptions of securities. We do not have a current specific plan for use of the proceeds, other than to fund operating losses.

      Pending application of the net proceeds as described above, the net proceeds of this offering will be deposited in interest bearing accounts or invested in certificates of deposit, United States government obligations or other short-term, high-quality debt instruments selected at our discretion.

DILUTION

      If you invest in our common stock, you will experience dilution to the extent of the difference between the public offering price per share of common stock you pay in this offering and the net tangible book value per share of our common stock immediately after this offering. Our net tangible book value as of June 30, 2005 was approximately $64.6 million, or $0.76 per share of common stock. Net tangible book value per share represents our total tangible assets as of June 30, 2005 (which excludes goodwill and other intangible assets), less our total liabilities, as of June 30, 2005 divided by the aggregate number of shares of our common stock outstanding as of June 30, 2005.

      After giving effect to the sale of the 16,539,253 million shares of our common stock in this offering, at an assumed offering price of $3.27 per share and after deducting discounts and the estimated offering expenses payable by us, our net tangible book value as of June 30, 2005 would have been approximately $116.6 million, or $1.15 per share. This represents an immediate increase in net tangible book value of $0.39 per share to existing stockholders and an immediate dilution of $2.12 per share to new investors. The following table illustrates the per share dilution that would occur in an offering with the above-described assumptions:

      The number of shares of common stock outstanding used for existing stockholders in the table and calculations above is based on 84,911,533 shares outstanding as of June 30, 2005 and excludes:

	•	options to purchase an aggregate of 9,026,384 shares of common stock having a weighted average exercise price of $2.45 per share, of which 8,256,588 have an exercise price less than the public offering price; and
	•	up to an aggregate of 3,657,112 additional shares available for issuance under currently authorized equity compensation plans and as additional shares that have been reserved for issuance in connection with equity compensation plans authorized in the future.

      The exercise of outstanding options having an exercise price less than the public offering price will increase dilution to new investors. If all of such outstanding options had been exercised as of June 30, 2005, the net tangible book value per share after this offering would have increased to approximately $1.26 per share and total dilution per share to new investors would be $2.09 per share.

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PLAN OF DISTRIBUTION

      We intend to sell the shares included in this offering directly to Monarch Pointe Fund, Ltd., a private investment fund managed by M.A.G. Capital, LLC, and to Asset Managers International Ltd, of Dublin, Ireland. We have entered into subscription agreements with these purchasers that establish an offering period of ten business days, October 10 to October 24, 2005, excluding October 13, 2005, during which we will sell shares to them. The agreements set the purchase price of any shares sold at 96% of the volume weighted average price of our common stock on the Nasdaq National Market on the day of the purchase, except that if on that day we sell any other shares under the shelf registration statement of which this prospectus supplement is a part at a lower price, the purchase price will be reduced to that lower price.

      The agreements provide that on the first business day of the period, the purchasers will purchase shares with an aggregate purchase price of $10,000,000. Prior to the opening of trading on each of the next nine days, we may require the purchasers to purchase shares on that day with a specified aggregate purchase price which may not exceed $7,500,000. If we do not specify an amount, the purchasers will purchase shares with an aggregate purchase price of $4,888,888.89. If at any time between 6:30 a.m. and 11:00 a.m. Pacific Time on any day during the offering period other than the first, the volume weighted average price of our common stock is less than 90% of that price on the preceding day, we will sell no shares to the purchasers on that day, except that we may waive this provision by giving notice to the purchasers prior to 11:00 a.m. Pacific Time on that day. For any day during the offering period that a purchase does not occur, an additional day will be added to the end of the offering period, up to a maximum of ten additional days.

      The agreements limit the aggregate number of shares that may be sold in the offering to the lesser of 17,000,000 or that number of shares that has an aggregate purchase price of $54,000,000. The agreements provide that the purchasers will not be permitted or required to purchase shares, to the extent that the purchase would cause either the purchasers managed by M.A.G. Capital, LLC, or Asset Managers International, Ltd., in each case, together with their affiliated parties, to beneficially own shares acquired pursuant to the subscription agreements of more than 9.99% of our outstanding common stock, as beneficial ownership is defined under Rule 13d-3 of the Securities Exchange Act of 1934, as amended.

      In June 2005, Capstone engaged Credit Suisse First Boston (“CSFB”) to be its exclusive financial advisor in connection with exploring various strategic alternatives. Pursuant to such engagement, CSFB will receive fees in the amount of 3.5% of the aggregate purchase price to be paid by the purchasers in the Offering. CSFB has earned $400,000 in fees to date in connection with such services.

LEGAL MATTERS

      Waller Lansden Dortch & Davis, PLLC, Nashville, Tennessee, has passed upon the validity of the shares of common stock offered by this prospectus supplement on our behalf.

WHERE YOU CAN FIND MORE INFORMATION

      We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any materials we file with the SEC at the SEC’s Public Reference Room at 450 Fifth Street, N.W., Washington, D.C. 20549. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. The SEC maintains an Internet site that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC at the SEC’s website at http://www.sec.gov.

      This prospectus supplement constitutes part of a registration statement on Form S-3 that we filed with the SEC under the Securities Act with respect to the securities offered hereby. As permitted by the rules and regulations of the SEC, this prospectus supplement omits some of the information, exhibits and undertakings included in the registration statement. You may read and copy the information omitted from

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      This prospectus supplement and the accompanying prospectus summarize material provisions of contracts and other documents that we refer you to. Since this prospectus supplement and the accompanying prospectus may not contain all the information that you may find important, you should review the full text of those documents. You should rely only on the information contained and incorporated by reference in this prospectus supplement and the accompanying prospectus.

      We make available free of charge through our website, which you can find at http://www.capstoneturbine.com, our annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and amendments to these reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC.

INCORPORATION OF DOCUMENTS BY REFERENCE

      We are incorporating by reference information we file with the SEC, which means:

	•	incorporated documents are considered part of this prospectus supplement;
	•	we can disclose important information to you by referring you to those documents; and
	•	information that we file later with the SEC automatically will update and supersede information contained in this prospectus supplement.

      We are incorporating by reference the following documents, which we have previously filed with the SEC:

      (a) our Annual Report on Form 10-K for the fiscal year ended March 31, 2005, filed with the SEC on June 29, 2005;

      (b) our Quarterly Report on Form 10-Q for the fiscal quarter ended June 30, 2005, filed with the SEC on August 9, 2005;

      (c) our Current Reports on Form 8-K, filed with the SEC on September 20, 2005, September 15, 2005, August 10, 2005, July 12, 2005, July 8, 2005 and July 6, 2005;

      (d) our Definitive Proxy Statement on Schedule 14A, filed with the SEC on August 4, 2005; and

      (e) any future filings with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act until our offering is completed; provided that this prospectus supplement will not incorporate any information we may furnish to the SEC under Item 2.02 or Item 7.01 of Form 8-K.

      The information incorporated by reference is deemed to be a part of this prospectus supplement, except for information incorporated by reference that is superseded by information contained in this prospectus supplement or any other document we subsequently file with the SEC that is incorporated or deemed to be incorporated by reference in this prospectus supplement. Likewise, any statement contained in this prospectus supplement, the accompanying prospectus or in a document incorporated or deemed to be incorporated by reference herein will be deemed to have been modified or superseded for purposes of this prospectus supplement and the accompanying prospectus to the extent that any statement contained in any document that we subsequently file with the SEC that is incorporated or deemed to be incorporated by reference herein modifies or supersedes the statement.

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      You can obtain copies of the documents incorporated by reference in this prospectus supplement but not delivered with this prospectus supplement without charge through our website (http://www.capstoneturbine.com) as soon as reasonably practicable after we electronically file the material with, or furnish it to, the SEC, or by requesting them in writing or by telephone at the following address:

	Capstone Turbine Corporation
	21211 Nordhoff Street
	Chatsworth, California 91311
	Attention: Walter J. McBride
	Executive Vice President, Chief Financial Officer and Secretary
	(818) 734-5300

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$150,000,000

Common Stock

Common Stock Warrants

Preferred Stock

Debt Securities

 

        We may from time to time offer, issue and sell, in one or more series, together or separately, the following:

	•	shares of our common stock;
	•	warrants to purchase shares of our common stock;
	•	shares of our preferred stock;
	•	debt securities, which may be either senior debt securities or subordinated debt securities, in each case consisting of notes or other evidence of indebtedness; or
	•	any combination of these securities, individually or as units.

      We will offer such securities at an aggregate public offering price of up to $150,000,000, or an equivalent amount in U.S. dollars if any securities are denominated in a currency other than U.S. dollars, on terms determined at the time we offer such securities. We may offer such securities separately or together, in separate classes or series, in amounts, at prices and on terms set forth in an applicable prospectus supplement to this prospectus.

      The applicable prospectus supplement will also contain information about any listing on a securities exchange of the securities covered by such prospectus supplement.

      We may sell these securities directly through agents designated from time to time by us, or to or through underwriters or dealers, or through a combination of these methods. We reserve the sole right to accept, and together with our agents, dealers and underwriters reserve the right to reject, in whole or in part, any proposed purchase of securities to be made directly or through agents, dealers or underwriters. If any agents, dealers or underwriters are involved in the sale of any of the securities, their names, and any applicable purchase price, fee, commission or discount arrangement between or among them, will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement. See “Plan of Distribution.” Our estimated net proceeds from the sale of securities also will be set forth in the relevant prospectus supplement. No securities may be sold without delivery of the applicable prospectus supplement describing the method and terms of the offering of such securities.

      Our common stock is listed on the Nasdaq National Market under the symbol “CPST.”

 

      Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

 

The date of this prospectus is September 14, 2005

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