Filed Pursuant to Rule 424(b)(5)

Registration No. 333-271389

PROSPECTUS SUPPLEMENT

(To the Prospectus Dated May 2, 2023)

ADVENT TECHNOLOGIES HOLDINGS, INC.

Up to $50,000,000

Common Stock

We have entered into an At The Market Offering Agreement with H.C. Wainwright & Co., LLC (“Wainwright”) relating to the sale of our common stock, $0.0001 par value per share (“Common Stock”), offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the At The Market Offering Agreement, we may offer and sell up to $50,000,000 of shares of our Common Stock from time to time through Wainwright acting as agent.

Sales of our Common Stock, if any, under this prospectus supplement and accompanying prospectus may be made in sales deemed to be “at the market equity offerings” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the “Securities Act”), including sales made directly on or through Nasdaq or any other existing trading market in the United States for our Common Stock, sales made to or through a market maker other than on an exchange or otherwise, directly to Wainwright as principal, in negotiated transactions at market prices prevailing at the time of sale or at prices related to such prevailing market prices and/or in any other method permitted by law. If we and Wainwright agree on any method of distribution other than sales of shares of our common stock on or through Nasdaq or another existing trading market in the United States at market prices, we will file a further prospectus supplement providing all information about such offering as required by Rule 424(b) under the Securities Act. Wainwright is not required to sell any specific dollar amount of shares but will use its commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us, consistent with its normal trading and sales practices and applicable laws and regulations, subject to the terms of the At The Market Offering Agreement on mutually agreed terms between Wainwright and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

Wainwright will be entitled to compensation at a fixed commission rate of 3.0% of the gross sales price per share sold under the At The Market Offering Agreement. In connection with the sale of our common stock on our behalf, Wainwright will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of Wainwright will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to Wainwright with respect to certain liabilities, including liabilities under the Securities Act.

We are an “emerging growth company” and a “smaller reporting company” under the federal securities laws and are subject to reduced public company reporting requirements. See “Prospectus Supplement Summary ‒ Emerging Growth Company” and ”‒ Smaller Reporting Company.” Our Common Stock and warrants are listed on the Nasdaq Capital Market under the symbols “ADN” and “ADNWW”, respectively. On June 1, 2023, the closing price of our Common Stock was $0.88 per share and the closing price of our warrants was $0.11 per share.

You should read this prospectus supplement and the accompanying prospectus, and the documents incorporated by reference in this prospectus supplement carefully before you invest.

Investing in our securities involves a high degree of risk. See the information contained under “Risk Factors” on page 5 of this prospectus supplement and in the related sections noted in the accompanying prospectus, and in the documents incorporated by reference herein and therein.

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

H.C. Wainwright & Co.

The date of this prospectus supplement is June 2, 2023.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a “shelf” registration statement on Form S-3 (File No. 333-271389) that we filed with the Securities and Exchange Commission, or the SEC, on April 21, 2023 and which became effective on May 2, 2023.

This prospectus supplement describes the specific terms of an offering of our Common Stock and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into the accompanying prospectus. The second part, the accompanying prospectus, provides more general information. If the information in this prospectus supplement is inconsistent with the accompanying prospectus or any document incorporated by reference therein filed prior to the date of this prospectus supplement, you should rely on the information in this prospectus supplement.

We have not authorized, and Wainwright has not authorized, anyone to provide you with any information or to make any representations other than those included or incorporated by reference in this prospectus supplement and the accompanying prospectus and any relevant free writing prospectus. If you receive any information not authorized by us, we take no responsibility for, and can provide no assurance as to the reliability of, such information. You should not assume that the information contained or incorporated by reference in this prospectus supplement or the accompanying prospectus or any relevant free writing prospectus is accurate as of any date other than its respective date.

It is important for you to read and consider all of the information contained in this prospectus supplement and the accompanying prospectus in making your investment decision. We include cross-references in this prospectus supplement and the accompanying prospectus to captions in these materials where you can find additional related discussions. The table of contents in this prospectus supplement provides the pages on which these captions are located. You should read both this prospectus supplement and the accompanying prospectus, together with the additional information described in the sections entitled “Where You Can Find More Information” and “Incorporation by Reference” of this prospectus supplement, before investing in our securities.

We are offering to sell, and seeking offers to buy, shares of Common Stock only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the Common Stock in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the Common Stock and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

References in this prospectus to the terms “we,” “us,” “our,” the “Company,” or other similar terms refer to Advent Technologies Holdings, Inc., a Delaware corporation, together with its consolidated subsidiaries.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus, any related free writing prospectus and the documents that we incorporate by reference herein or therein contain forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Our forward-looking statements include, but are not limited to, statements regarding our or our management team’s expectations, hopes, beliefs, intentions or strategies regarding the future. In addition, any statements that refer to projections, forecasts or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intends,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. Forward-looking statements in this prospectus supplement may include, for example, statements about:

These forward-looking statements are based on information available as of the date of this prospectus supplement, and current expectations, forecasts and assumptions, and involve a number of judgments, risks and uncertainties. Important factors could cause actual results to differ materially from those indicated or implied by forward-looking statements such as those contained in documents we have filed with the SEC. Accordingly, forward-looking statements should not be relied upon as representing our views as of any subsequent date, and we do not undertake any obligation to update forward-looking statements to reflect events or circumstances after the date they were made, whether as a result of new information, future events or otherwise, except as may be required under applicable securities laws.

As a result of a number of known and unknown risks and uncertainties, our actual results or performance may be materially different from those expressed or implied by these forward-looking statements. For a discussion of the risks involved in our business and investing in our Common Stock, see the section entitled “Risk Factors.”

Should one or more of these risks or uncertainties materialize, or should any of the underlying assumptions prove incorrect, actual results may vary in material respects from those expressed or implied by these forward-looking statements. You should not place undue reliance on these forward-looking statements.

RISK FACTORS

Investing in our securities is speculative and involves a high degree of risk. You should carefully consider the risks set out below and the other documents incorporated by reference in this prospectus supplement that summarize the risks that may materially affect us and our business before making an investment in our securities. Please see “Incorporation by Reference”. If any of these risks occur, our business, results of operations or financial condition could be materially adversely affected. In that case, the trading price of our securities could decline, and you may lose all or part of your investment. The risks set out in this prospectus supplement are not the only risks we face. You should also refer to the other information set forth in this prospectus supplement as well as those incorporated by reference herein and therein, including financial statements and the related notes, for further risks faced by us.

The Company and its securities should be considered a speculative investment due to the high-risk nature of our business, and you should carefully consider all of the information disclosed in this prospectus supplement, the accompanying prospectus and the documents incorporated herein and therein prior to making an investment in the Company. In addition, the following risk factors should be given special consideration when evaluating an investment in the securities.

Risks Related to the Business

We have incurred losses since inception and we expect that we will continue to incur losses for the foreseeable future.

We have not been profitable since operations commenced, and we may never achieve or sustain profitability. We expect to continue to incur net losses and generate negative cash flows until we can produce sufficient revenues and gross profit to cover our costs. We may never become profitable. Even if we do achieve profitability, we may be unable to sustain or increase our profitability in the future. We will require significant additional capital to continue operations and to implement our business strategy. We cannot estimate with reasonable certainty the actual amounts necessary to successfully complete the development, manufacture and commercialization of our products and there is no certainty that we will be able to raise the necessary capital on reasonable terms or at all.

Our audited financial statements included a statement that there is a substantial doubt about our ability to continue as a going concern and a continuation of negative financial trends could result in our inability to continue as a going concern.

Our audited financial statements as of and for the year ended December 31, 2022 were prepared on the assumption that we would continue as a going concern. Our audited financial statements as of and for the year ended December 31, 2022 did not include any adjustments that might result from the outcome of this uncertainty. Our management has determined that there is a substantial doubt about our ability to continue as a going concern over the next twelve months based on the insufficient amount of cash and cash equivalents as of the financial statement filing date and our independent auditors have included a “going concern” explanatory paragraph in their report on our financial statements as of and for the year ended December 31, 2022. In July 2022, we received official ratification from the European Commission of the European Union for one of the Important Projects of Common European Interest (“IPCEI”), Green HiPo. This project provides for the availability of funding of €782.1 million over the next six years. As of the issuance date of the consolidated financial statements, we have not received an agreement which provides the terms of the funding. In addition to Green HiPo, management may pursue additional capital raises in the future. We cannot provide assurance that we will be able to obtain additional funding on acceptable terms, if at all. If we are unable to obtain sufficient funding, we could be required to delay our development efforts, limit activities and reduce research and development costs, which could adversely affect its business prospects. The reaction of investors to the inclusion of a going concern statement by our independent auditors, and our potential inability to continue as a going concern, could materially adversely affect the price of our Common Stock.

We continue to generate a low level of revenue from our core products.

Based on conversations with existing customers and incoming inquiries from prospective customers, we anticipate substantial increased demand for our MEAs and fuel cell systems from a wide range of customers as we scale up our production facilities and testing capabilities, and as the awareness of our MEA capabilities becomes widely known in the industry. We expect both existing customers to increase order volume, and to generate substantial new orders from new customers, with some of whom we are already in discussions regarding prospective commercial partnerships and joint development agreements. As of December 31, 2022, we were still generating a low level of revenues compared to our future projections and have not made any commercial sales to new customers.

Risks Related to the Offering

A return on the Common Stock purchased in this offering is not guaranteed.

There is no guarantee that the shares of Common Stock purchased in this offering will earn any positive return in the short term or long term. Investing in our Common Stock is speculative and involves a high degree of risk and should be undertaken only by holders whose financial resources are sufficient to enable them to assume such risks and who have no need for immediate liquidity in their investment. Investing in our securities is appropriate only for holders who have the capacity to absorb a loss of some or all of their holdings.

We may not be able to maintain compliance with the continued listing requirements of the Nasdaq Capital Market.

Our common stock is listed on the Nasdaq Capital Market. To maintain that listing, we must satisfy minimum financial and other requirements including, without limitation, a requirement that our closing bid price be at least $1.00 per share.

On May 24, 2023, we were notified by Nasdaq Listing Qualifications Staff about bid price deficiency. The Company is reviewing plans to regain compliance with the $1.00 closing bid price requirement. If the Company does not regain compliance with the bid price requirement by November 30, 2023, the Company may be eligible for an additional 180-calendar day compliance period so long as it satisfies the criteria for initial listing on the Nasdaq Capital Market and the continued listing requirement for market value of publicly held shares and the Company provides written notice to Nasdaq of its intention to cure the deficiency during the second compliance period by effecting a reverse stock split, if necessary. If we fail to continue to meet all applicable continued listing requirements for The Nasdaq Capital Market in the future and Nasdaq determines to delist our common stock, the delisting could adversely affect the market liquidity of our common stock, our ability to obtain financing to repay debt and fund our operations.

We currently do not have enough authorized shares of common stock to issue all shares offered hereunder and we require stockholder approval and the subsequent filing with the Secretary of State of the State of Delaware a certificate of amendment to our second amended and restated certificate of incorporation to effect an increase of the authorized number of shares of common stock available for issuance under the At The Market Offering Agreement. There is no assurance that such stockholder approval will be obtained which will limit our ability to raise capital and could materially and adversely affect the Company’s business, financial condition and results of operations.

We do not have enough shares of Common Stock currently authorized under our second amended and restated certificate of incorporation (the “certificate of incorporation”) to issue all shares in the offering to pursuant to the At the Market Offering Agreement. We currently have 110,000,000 shares of common stock authorized under our certificate of incorporation. As of June 1, 2023, we had 53,097,236 shares of Common Stock issued and outstanding, 26,369,557 shares issuable upon exercise of outstanding warrants, 3,289,855 shares issuable upon exercise of outstanding options, 2,288,772 shares issuable upon vesting of outstanding restricted stock units,33,671 shares issuable upon outstanding restricted stock units that have vested, and 295,196 shares available for future issuance as awards under the Company’s 2021 Equity Incentive Plan. We currently do not have sufficient remaining authorized shares of Common Stock to fully utilize sales pursuant to the At The Market Offering Agreement unless and until an increase of our authorized shares of Common Stock is approved by stockholders and we file with the Secretary of State of the State of Delaware a certificate of amendment to our certificate of incorporation effecting such increase. If our stockholders do not approve the increase of authorized shares of Common Stock, our business development and financing alternatives will be limited by the lack of sufficient unissued and unreserved authorized shares of Common Stock, and stockholder value may be harmed, perhaps severely, by this limitation.

We have used almost all of our unreserved, authorized shares.

We have currently used almost all of our unreserved authorized shares and will need stockholder approval to implement an increase in our authorized shares of common stock. Our certificate of incorporation and the Delaware General Corporation Law (the “DGCL”), currently require the approval of stockholders holding not less than a majority of all outstanding shares of capital stock entitled to vote in order to approve an increase in our authorized shares of common stock. We currently plan to seek stockholder approval at our annual meeting, which is scheduled to be held on June 13, 2023. There are no assurances that stockholder approval will be obtained, in which event will be unable to raise additional capital through the issuance of shares of common stock to fund our future operations.

We have broad discretion in the use of proceeds from the offering.

Our management will have broad discretion with respect to the application of net proceeds received by us from the sale of the shares under this prospectus supplement and may spend such proceeds in ways that do not improve our results of operations or enhance the value of the securities. Any failure by management to apply these funds effectively could result in financial losses that could have a material adverse effect on our business or cause the price of our common shares to decline.

The Common Stock offered hereby will be sold in “at the market” offerings, and investors who buy shares at different times will likely pay different prices.

Investors who purchase shares in this offering at different times will likely pay different prices, and so may experience different outcomes in their investment results. We will have discretion, subject to market demand, to vary the timing, prices, and numbers of shares sold, and there is no maximum sales price. Pursuant to the At The Market Offering Agreement, our board of directors, or a duly authorized executive committee thereof, may authorize, from time to time, a minimum sales price per share of our common stock sold in this offering, which will limit the Company’s ability to make sales if the price goes below that minimum. Investors may experience a decline in the value of their shares as a result of share sales made at prices lower than the prices they paid.

You may experience immediate and substantial dilution in the net tangible book value per share of the Common Stock you purchase.

The price per share of our Common Stock being offered may be higher than the net tangible book value per share of our Common Stock outstanding prior to your purchase and in such case, you will suffer immediate dilution based on the difference between the price you pay per share of our Common Stock and our net tangible book value per share at the time of your purchase.

The actual number of shares we will issue and the total aggregate proceeds resulting from sales made under the At The Market Offering Agreement with Wainwright, at any one time or in total, is uncertain.

Subject to certain limitations in the At The Market Offering Agreement with Wainwright and compliance with applicable law, we have the discretion to deliver sales notices to Wainwright at any time throughout the term of the At The Market Offering Agreement. The number of shares that are sold by Wainwright after delivering a sales notice will fluctuate based on the market price of the Common Stock during the sales period and limits we set with Wainwright, and as such, it is not currently possible to predict the aggregate proceeds to be raised in connection with this offering or the number of shares that will ultimately be issued.

Future issuances of securities may result in substantial dilution to our existing stockholders and investors.

We may issue or sell additional shares of Common Stock or other securities that are convertible or exchangeable into shares of Common Stock in subsequent offerings or may issue additional shares of Common Stock or other securities to finance future acquisitions. We cannot predict the size or nature of future sales or issuances of securities or the effect, if any, that such future sales and issuances will have on the market price of the shares. Sales or issuances of substantial numbers of shares of Common Stock or other securities that are convertible or exchangeable into Common Stock, or the perception that such sales or issuances could occur, may adversely affect prevailing market prices of the Common Stock. With any additional sale or issuance of shares of Common Stock or other securities that are convertible or exchangeable into Common Stock, our stockholders will suffer dilution to their voting power and economic interest in the Company. Furthermore, to the extent holders of our stock options, warrants or other convertible securities convert or exercise their securities and sell the shares of Common Stock they receive, the trading price of the Common Stock on Nasdaq may decrease due to the additional amount of shares available in the market.

The market price of our Common Stock may be volatile.

The market price of our Common Stock may be volatile and subject to wide fluctuations in response to numerous factors, many of which are beyond our control. This volatility may affect the ability of holders of Common Stock to sell their securities at an advantageous price. Market price fluctuations in our Common Stock may be due to our operating results failing to meet expectations of securities analysts or investors in any period, downward revision in securities analysts’ estimates, adverse changes in general market conditions or economic trends, acquisitions, dispositions or other material public announcements by us or our competitors, along with a variety of additional factors. These broad market fluctuations may adversely affect the market price of the Common Stock.

Financial markets have periodically at times experienced significant price and volume fluctuations that have particularly affected the market prices of equity securities of companies and that have often been unrelated to the operating performance, underlying asset values or prospects of such companies. Accordingly, the market price of our Common Stock may decline even if our operating results, underlying asset values or prospects have not changed. Additionally, these factors, as well as other related factors, may cause decreases in asset values that are deemed to be other than temporary, which may result in impairment losses. There can be no assurance that continuing fluctuations in price and volume will not occur. If such increased levels of volatility and market turmoil continue, our operations could be adversely impacted, and the trading price of our Common Stock may be materially adversely affected.

Sales of a significant number of shares of our Common Stock in the public markets, or the perception that such sales could occur, could depress the market price of our Common Stock.

Sales of a significant number of shares of our Common Stock in the public markets, or the perception that such sales could occur as a result of our utilization of a universal shelf registration statement, our At The Market Offering Agreement with Wainwright or otherwise, could depress the market price of our Common Stock and impair our ability to raise capital through the sale of additional equity securities. We cannot predict the effect that future sales of our Common Stock or the market perception that we are permitted to sell a significant number of our securities would have on the market price of our Common Stock.

Resales of our Common Stock in the public market during this offering by our stockholders may cause the market price of our Common Stock to fall.

We may issue shares of Common Stock from time to time in connection with this offering. The issuance from time to time of these new shares of Common Stock, or our ability to issue new shares of Common Stock in this offering, could result in resales of shares our Common Stock by our current stockholders concerned about the potential dilution of their holdings. In turn, these resales could have the effect of depressing the market price for our Common Stock.

A liquid market in our Common Stock on Nasdaq may not be maintained.

Our stockholders may be unable to sell significant quantities of Common Stock into the public trading markets without a significant reduction in the price of their shares, or at all. There can be no assurance that there will be sufficient liquidity of the Common Stock on the trading market, and that we will continue to meet the listing requirements of Nasdaq or achieve listing on any other national securities exchange. There can be no assurance that an active and liquid market for our Common Stock will be maintained, and our stockholders may find it difficult to resell shares of Common Stock.

USE OF PROCEEDS

We may issue and sell shares of Common Stock having aggregate sales proceeds of up to $50,000,000 from time to time, before deducting sales agent commissions and expenses. The amount of proceeds from this offering will depend upon the number of shares of our Common Stock sold and the market price at which they are sold. There can be no assurance that we will be able to sell any shares under or fully utilize the At The Market Offering Agreement with Wainwright.

We intend to use the net proceeds to fund the operating expenses and capital expenses for product development and plan to make substantial investments over the next several years, among others, in new production equipment and warehousing, systems assembly line, MEA assembly automation, aeronautical stacks, facility expansion, new hirings and for working capital and general corporate purposes. Accordingly, we will have broad discretion in the application of the proceeds of this offering. We incurred operating losses and negative operating cash flow for the year ended December 31, 2022 and for the three months ended March 31, 2023. The Company expects to use the net proceeds from the offering in pursuit of its ongoing general business objectives. To that end, a substantial portion of the net proceeds from the offering are expected to be allocated to working capital requirements. To the extent that we have negative operating cash flows in future periods, we may need to deploy a portion of the net proceeds from the offering and/or our existing working capital to fund such negative cash flow.

Our ultimate use might vary substantially from what is stated in this prospectus supplement and will depend on a number of factors, including those referred to under “Risk Factors” in the accompanying prospectus and any other factors set forth in this prospectus supplement.

The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of any collaborative or strategic partnering efforts, and the competitive environment for our products. As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses for the net proceeds to us from this offering. Accordingly, our management will have broad discretion in the timing and application of these proceeds.

All expenses relating to the offering under this prospectus supplement will be paid out of the gross proceeds of the offering.

PLAN OF DISTRIBUTION

We have entered into an At The Market Offering Agreement with Wainwright, pursuant to which we may issue and sell from time to time shares of our Common Stock having an aggregate offering price of up to $50,000,000 through Wainwright as our sales agent pursuant to this prospectus supplement and the accompanying prospectus. Sales of the shares of Common Stock, if any, will be made by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415 promulgated under the Securities Act. If we and Wainwright agree on any method of distribution other than sales of shares on or through Nasdaq or another existing trading market in the United States at market prices, we will file a further prospectus supplement providing all information about such offering as required by Rule 424(b) under the Securities Act.

Wainwright will offer shares of our Common Stock at prevailing market prices subject to the terms and conditions of the At The Market Offering Agreement as agreed upon by us and Wainwright. We will designate the number of shares which we desire to sell, the time period during which sales are requested to be made, any limitation on the number of shares that may be sold in one day and any minimum price below which sales may not be made. Subject to the terms and conditions of the At The Market Offering Agreement, Wainwright will use its commercially reasonable efforts consistent with its normal trading and sales practices to sell on our behalf all of the shares requested to be sold by us. We or Wainwright may suspend the offering of the shares of Common Stock being made through Wainwright under the At The Market Offering Agreement upon proper notice to the other party.

Settlement for sales of Common Stock will occur on the second trading day or such shorter settlement cycle as may be in effect under Exchange Act Rule 15c6-1 from time to time, following the date on which any sales are made, or on some other date that is agreed upon by us and Wainwright in connection with a particular transaction, in return for payment of the net proceeds to us. Sales of our shares of our Common Stock as contemplated in this prospectus supplement and the accompanying prospectus will be settled through the facilities of The Depository Trust Company or by such other means as we and Wainwright may agree upon. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

We will pay Wainwright in cash, upon each sale of shares of our common stock pursuant to the At The Market Offering Agreement, a commission of 3.0% of the gross proceeds from each sale of shares. Because there is no minimum offering amount required as a condition to this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. Pursuant to the terms of the At The Market Offering Agreement, we agreed to reimburse Wainwright for the documented fees and costs of its legal counsel reasonably incurred in connection with entering into the transactions contemplated by the At The Market Offering Agreement in an amount not to exceed $50,000 in the aggregate, in addition to up to a maximum of $2,500 per due diligence update session conducted in connection with each such date the Company files its Quarterly Reports on Form 10-Q. We will report at least quarterly the number of shares of our Common Stock sold through Wainwright under the At The Market Offering Agreement, the net proceeds to us and the compensation paid by us to Wainwright in connection with the sales of shares of our Common Stock.

In connection with the sales of shares of our Common Stock on our behalf, Wainwright will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to Wainwright will be deemed to be underwriting commissions or discounts. We have agreed in the At The Market Offering Agreement to provide indemnification and contribution to Wainwright against certain liabilities, including liabilities under the Securities Act.

The offering of our shares of our Common Stock pursuant to the At The Market Offering Agreement will terminate upon the earlier of the sale of all of the shares of our Common Stock provided for in this prospectus supplement or termination of the At The Market Offering Agreement as permitted therein.

To the extent required by Regulation M, Wainwright will not engage in any market making activities involving our Common Stock while the offering is ongoing under this prospectus supplement.

From time to time, Wainwright may provide in the future various advisory, investment and commercial banking and other services to us in the ordinary course of business, for which they may receive customary fees and commissions. However, we have no present arrangements with Wainwright for any further services.

This prospectus supplement and the accompanying prospectus may be made available in electronic format on a website maintained by Wainwright, and Wainwright may distribute this prospectus supplement and the accompanying prospectus electronically.

The foregoing does not purport to be a complete statement of the terms and conditions of the At The Market Offering Agreement. A copy of the At The Market Offering Agreement is included as an exhibit to our Current Report on Form 8-K that will be filed with the SEC and incorporated by reference into the registration statement of which this prospectus supplement and the accompanying prospectus form a part. See “Where You Can Find More Information” and “Incorporation of Documents By Reference”.

Trading Market

Our Common Stock is listed on Nasdaq under the symbol “ADN.”

LEGAL MATTERS

Certain legal matters relating to this offering and the validity of the Common Stock offered by this prospectus supplement are being passed upon for Advent Technologies Holdings, Inc. by Manatt, Phelps & Phillips, LLP, Los Angeles, California. Wainwright is being represented by Ellenoff Grossman & Schole LLP, New York, New York.

EXPERTS

The consolidated financial statements of Advent Technologies Holdings, Inc. appearing in Advent Technologies Holdings, Inc.’s Annual Report (Form 10-K) for the year ended December 31, 2022, have been audited by Ernst & Young (Hellas) Certified Auditors Accountants S.A., independent registered public accounting firm, as set forth in their report thereon, (which contains an explanatory paragraph describing conditions that raise substantial doubt about the Company’s ability to continue as a going concern as described in Note 1 to the consolidated financial statements), included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing. Ernst & Young (Hellas) Certified Auditors Accountants S.A. is located at Chimarras 8B, 15125, Maroussi, Athens, Greece and is registered as a corporate body with the public register for company auditors-accountants kept with the Body of Certified Auditors-Accountants, or SOEL, Greece with registration number 107.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the securities offered by this prospectus and the applicable prospectus supplement. This prospectus and the applicable prospectus supplement do not contain all of the information set forth in the registration statement and its exhibits and schedules in accordance with SEC rules and regulations. For further information with respect to us and the securities being offered by this prospectus and the applicable prospectus supplement, you should read the registration statement of which this prospectus is a part, including its exhibits and schedules. Statements contained in this prospectus and the applicable prospectus supplement, including documents that we have incorporated by reference, as to the contents of any contract or other document referred to are not necessarily complete, and, with respect to any contract or other document filed as an exhibit to the registration statement or any other such document, each such statement is qualified in all respects by reference to the corresponding exhibit. You should review the complete contract or other document to evaluate these statements. You may obtain copies of the registration statement and its exhibits via the SEC’s EDGAR database or our website.

We file annual, quarterly and current reports, proxy statements and other documents with the SEC under the U.S. Securities Exchange Act of 1934, as amended, or the Exchange Act. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers, including us, that file electronically with the SEC. You may obtain documents that we file with the SEC at www.sec.gov.

We also make these documents available on our website at https://www.advent.energy. Our website and the information contained or connected to our website is not incorporated by reference in this prospectus or any prospectus supplement, and you should not consider it part of this prospectus or any prospectus supplement.

INCORPORATION BY REFERENCE

The SEC allows us to incorporate by reference the information and reports we file with it, which means that we can disclose important information to you by referring you to these documents. The information incorporated by reference is an important part of this prospectus supplement, and information that we file later with the SEC will automatically update and supersede the information already incorporated by reference. We are incorporating by reference the documents listed below, which we have already filed with the SEC (SEC File No. 001-38742), and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including all filings made after the date of the filing of this prospectus supplement, except as to any portion of any future report or document that is not deemed filed under such provision, after the date of this prospectus supplement and prior to the termination of this offering:

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We incorporate by reference any future filings made with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act between the date of this prospectus supplement and the termination of the offering.

Notwithstanding the foregoing, unless specifically stated to the contrary, information that we furnish (and that is not deemed “filed” with the SEC) under Items 2.02 and 7.01 of any Current Report on Form 8-K, including the related exhibits under Item 9.01, is not incorporated by reference into this prospectus supplement or the registration statement of which this prospectus supplement is a part.

Any statement contained in a document that is incorporated by reference will be modified or superseded for all purposes to the extent that a statement contained in this prospectus supplement, or in any other document that is subsequently filed with the SEC and incorporated by reference into this prospectus supplement, modifies or is contrary to that previous statement. Any statement so modified or superseded will not be deemed a part of this prospectus supplement, except as so modified or superseded. Since information that we later file with the SEC will update and supersede previously incorporated information, you should look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus supplement or in any documents previously incorporated by reference have been modified or superseded.

Upon request, we will provide, without charge, to each person, including any beneficial owner, to whom a copy of this prospectus supplement is delivered, a copy of the documents incorporated by reference into this prospectus supplement but not delivered therewith. You may request a copy of these filings, and any exhibits we have specifically incorporated by reference as an exhibit in this prospectus supplement, at no cost by writing or telephoning us at the following address: Advent Technologies Holdings, Inc., 500 Rutherford Avenue, Suite 102, Boston, MA 02129, Attention: Corporate Secretary; or by telephone at (617) 655-6000.

You may also access these documents, free of charge on the SEC’s website at www.sec.gov or on our website at https://www.advent.energy. Information contained on our website is not incorporated by reference into this prospectus supplement and you should not consider any information on, or that can be accessed from, our website as part of this prospectus supplement.

This prospectus supplement is part of a registration statement we filed with the SEC. We have incorporated exhibits into this registration statement. You should read the exhibits carefully for provisions that may be important to you.

You should rely only on the information incorporated by reference or provided in this prospectus supplement. We have not authorized anyone to provide you with different information. We are not making an offer of these securities in any state where the offer is not permitted. You should not assume that the information in this prospectus supplement or in the documents incorporated by reference is accurate as of any date other than the date on the front of this prospectus supplement or those documents.

Up to $50,000,000 of Common Stock

Prospectus Supplement

H.C. Wainwright & Co.

June 2, 2023

PROSPECTUS

$200,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Rights

Units

From time to time, we may offer to sell the securities described in this prospectus separately or together in any combination, in one or more classes or series, in amounts, at prices, and on terms to be determined at the time of any such offering. The aggregate offering price of the securities we sell pursuant to this prospectus will not exceed $200,000,000.

This prospectus provides a general description of the securities that we may offer. Each time any securities are offered pursuant to this prospectus, we will provide specific information about the offered securities in one or more supplements to this prospectus.

Prospectus supplements may also add, update or change information in this prospectus. If the information varies between this prospectus and any accompanying prospectus supplement, you should rely on the information in the prospectus supplement.

Our common stock and warrants are listed on Nasdaq under the symbols “ADN” and “ADNWW”, respectively. Any prospectus supplement will indicate if the securities offered thereby will be listed on any securities exchange.

You should carefully read this prospectus and any applicable prospectus supplement, together with the documents we incorporate by reference, before you invest in our securities. This prospectus may not be used to offer and sell our securities unless accompanied by a prospectus supplement describing the method and terms of the offering.

Investing in any of our securities involves a high degree of risk. Please read carefully the section entitled “Risk Factors” on page 3 of this prospectus and the “Risk Factors” section contained in any applicable prospectus supplement and in the documents incorporated by reference in this prospectus before investing in our securities.

We are an “emerging growth company” and a “smaller reporting company” as such terms are defined under the federal securities laws and, as such, are subject to certain reduced public company reporting requirements.

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 May 2, 2023

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, using a “shelf” registration process. Under this shelf registration process, we may, from time to time, sell any combination of the securities described in this prospectus in one or more offerings.

This prospectus provides you with a general description of the securities that may be offered pursuant to the registration statement of which this prospectus forms a part. Each time we sell securities pursuant to the registration statement of which this prospectus forms a part, a prospectus supplement will be provided that contains specific information about the terms of that offering and the securities being sold in that offering. The prospectus supplement may also add to, update or change the information contained in or incorporated by reference in this prospectus. If information varies between this prospectus and any prospectus supplement, you should rely on the information in the prospectus supplement.

You should only rely on the information contained in or incorporated by reference in this prospectus, any prospectus supplement and any free writing prospectus prepared by or on behalf of us or to which we have referred you. We have not authorized anyone to provide you with different information. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making offers to sell the securities described in this prospectus in any jurisdiction in which an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

Before purchasing any securities, you should carefully read both this prospectus and any prospectus supplement, together with the additional information described under the heading “Where You Can Find Additional Information” and “Information We Incorporate by Reference.” You should assume that the information contained in this prospectus, any prospectus supplement or any free writing prospectus is accurate only as of the date on its respective cover, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, unless we indicate otherwise. Our business, financial condition, results of operations, and prospects may have changed materially since those dates.

References in this prospectus to the terms “we,” “us,” “our,” “the Company,” or other similar terms refer to Advent Technologies Holdings, Inc., a Delaware corporation, together with its consolidated subsidiaries.

WHERE YOU CAN FIND ADDITIONAL INFORMATION

This prospectus is part of a registration statement on Form S-3 that we filed with the SEC. This prospectus does not contain all of the information included in the registration statement.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. We have also filed a registration statement on Form S-3, including exhibits, under the Securities Act, with respect to the common stock and warrants offered by this prospectus. This prospectus is part of the registration statement, but does not contain all of the information included in the registration statement or the exhibits. Our SEC filings are available to the public on the internet at a website maintained by the SEC located at http://www.sec.gov.

We also maintain an Internet website at http://www.advent.energy. Through our website, we make available, free of charge, the following documents as soon as reasonably practicable after they are electronically filed with, or furnished to, the SEC: our Annual Reports on Form 10-K; our proxy statements for our annual and special shareholder meetings; our Quarterly Reports on Form 10-Q; our Current Reports on Form 8-K; Forms 3, 4 and 5 and Schedules 13D; and amendments to those documents. The information contained on, or that may be accessed through, our website is not part of, and is not incorporated into, this prospectus.

Forms of any documents establishing the terms of the offered securities are filed as exhibits to the registration statement of which this prospectus forms a part or will be filed through an amendment to our registration statement on Form S-3 or under cover of a Current Report on Form 8-K or other document filed with the SEC and incorporated into this prospectus by reference. Statements in this prospectus about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. The full registration statement, including exhibits thereto, may be obtained from either the SEC or us as indicated above.

INFORMATION WE INCORPORATE BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be part of this prospectus. Any statement contained in a document incorporated or deemed to be incorporated by reference in this prospectus will be deemed to be modified or superseded for purposes of this prospectus to the extent a statement contained in this prospectus or in any other subsequently filed document that is or is deemed to be incorporated by reference in this prospectus modifies or supersedes that statement.

This prospectus and any accompanying prospectus supplement incorporate by reference the documents set forth below that have previously been filed with the SEC:

We also incorporate by reference the information contained in all other documents that we file with the SEC pursuant to Sections 13(a), 13(c), 14, or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act (other than the portions that are deemed to have been furnished and not filed in accordance with SEC rules, unless otherwise indicated therein), on or after the date of the registration statement of which this prospectus forms a part and prior to its effectiveness and prior to the completion of the offering of all securities under this prospectus and any prospectus supplement. The information contained in any such document will be considered part of this prospectus from the date the document is filed with the SEC. Any statement contained in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this prospectus and any accompanying prospectus supplement to the extent that a statement contained herein or therein or in any other subsequently filed document, which also is or is deemed to be incorporated by reference herein or therein modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus or any accompanying prospectus supplement. We will provide to each person, including any beneficial owner, to whom a prospectus (or a notice of registration in lieu thereof) is delivered, a copy of any or all of the documents incorporated by reference in this prospectus or any accompanying prospectus supplement (other than an exhibit to these filings, unless the exhibit is specifically incorporated by reference in the document requested) at no cost. Any such request can be made by writing or telephoning us at the following address and telephone number:

Advent Technologies Holdings, Inc.

Corporate Secretary

500 Rutherford Avenue, Suite 102

Boston, MA 02129

(617) 655-6000

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents to which the Company refers you to in this prospectus, as well as oral statements made or to be made by the Company, include certain “forward-looking statements” within the meaning of, and subject to the safe harbor created by, the Private Securities Litigation Reform Act of 1995 and other federal securities laws, which are referred to as the safe harbor provisions, with respect to the businesses, strategies and plans of the Company and its expectations relating to its future financial condition and performance. Statements included in this prospectus that are not historical facts are forward-looking statements, including statements about the beliefs and expectations of the management of the Company. Words such as “believe,” “continue,” “could,” “expect,” “plan,” “anticipate,” “intends,” “estimate,” “forecast,” “project,” “potential,” “predict”, “should,” “may,” “might,” “will,” “would” or the negative thereof and similar expressions are intended to identify such forward-looking statements that are intended to be covered by the safe harbor provisions.

Any forward-looking statements in this prospectus, any prospectus supplement, and the information incorporated by reference in this prospectus and each prospectus supplement reflect our current views with respect to future events or to our future financial performance and involve known and unknown risks, uncertainties, and other factors that may cause our actual results, performance, or achievements to be materially different from any future results, performance, or achievements expressed or implied by these forward-looking statements. Factors that may cause actual results to differ materially from current expectations include, among other things, those described under the heading “Risk Factors” in our most recent Annual Report on Form 10-K filed with the SEC, as supplemented by our Quarterly Reports on Form 10-Q, and discussed elsewhere in this prospectus, each prospectus supplement, and the information incorporated by reference in this prospectus and each prospectus supplement. Given these uncertainties, you should not place undue reliance on these forward-looking statements.

All subsequent written or oral forward-looking statements attributable to the Company are expressly qualified in their entirety by the cautionary statements contained or referred to in this section. The Company is not under any obligation, and the Company expressly disclaims any obligation, to update, alter, or otherwise revise any forward-looking statements, whether written or oral, that may be made from time to time, whether as a result of new information, future events or otherwise, except as may be required by law.

RISK FACTORS

Investing in any of our securities involves significant risks. Before making an investment decision, in addition to the other information contained in or incorporated by reference in this prospectus and any prospectus supplement, you should carefully consider the specific risks set forth under the heading “Risk Factors” in our most recent Annual Report on Form 10-K filed with the SEC, as such risk factors may be amended, supplemented, or superseded from time to time by other reports we file with the SEC, including subsequent Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q, and the risk factors described under the caption “Risk Factors” in any applicable prospectus supplement. See “Where You Can Find Additional Information” and “Information We Incorporate by Reference.” If any of these risks actually occurs, our business, results of operations, and financial condition could suffer. In that case, the trading price of our securities could decline, and you could lose all or part of your investment. Additional risks and uncertainties not currently known to us, or that we currently believe are immaterial, may also adversely affect our business, operating results, and financial condition and the value of an investment in our securities. In addition, past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods.

USE OF PROCEEDS

We intend to use the net proceeds from the sale of the securities as set forth in the applicable prospectus supplement.

DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock, and certain provisions of our amended and restated certificate of incorporation and amended and restated bylaws, are summaries of material terms and provisions and are qualified by reference to our amended and restated certificate of incorporation and our amended and restated bylaws, copies of which have been filed with the SEC and are incorporated by reference as exhibits to the registration statement of which this prospectus forms a part.

Authorized and Outstanding Capital Stock

Pursuant to our second amended and restated certificate of incorporation (the “Charter”), the total number of shares of capital stock that we are authorized to issue is 111,000,000 shares, consisting of two classes as follows: (i) 110,000,000 shares of common stock, par value $0.0001 per share (the “common stock”), and (ii) 1,000,000 shares of preferred stock, par value $0.0001 per share.

As of March 31, 2023, there were approximately 31 holders of record of shares of our common stock and 2 holders of record of our warrants. Such numbers do not include DTC participants or beneficial owners holding shares through nominee names.

Common Stock

Voting Rights. Except as otherwise required by law or the second amended and restated certificate of incorporation, holders of common stock are entitled to one vote for each share of common stock held of record by such holder on all matters on which stockholders are generally entitled to vote; provided, that, except as otherwise required by law, holders of common stock shall not be entitled to vote on any amendment to the second amended and restated certificate of incorporation that relates solely to the terms of one or more outstanding series of preferred stock if the holders of such affected series of preferred stock are entitle, either separately or together with the holders of one or more other such series of preferred stock, to vote thereon pursuant to the second amended and restated certificate of incorporation or the DGCL.

Dividend Rights. The board of directors may from time to time declare, and the Company may pay, dividends (payable in cash, property or shares of capital stock) on the Company’s outstanding shares of capital stock, subject to applicable law and the second amended and restated certificate of incorporation.

Liquidation, Dissolution, and Winding Up. On the liquidation, dissolution, distribution of assets or winding up of the Company, each holder of shares of common stock will be entitled, pro rata on a per share basis, to all assets of the Company of whatever kind available for distribution to the holders of common stock, subject to the designations, preferences, limitations, restrictions and relative rights of any other class or series of preferred stock then outstanding.

Preemptive or Other Rights

Our stockholders have no preemptive or other subscription rights and there are no sinking fund or redemption provisions applicable to our common stock.

Preferred Stock

Our second amended and restated certificate of incorporation provides that shares of preferred stock may be issued from time to time in one or more series. Our board of directors will be authorized to fix the voting rights, if any, designations, powers, preferences, the relative, participating, optional or other special rights and any qualifications, limitations and restrictions thereof, applicable to the shares of each series. Our board of directors will be able to, without stockholder approval, issue preferred stock with voting and other rights that could adversely affect the voting power and other rights of the holders of the common stock and could have anti-takeover effects. The ability of our board of directors to issue preferred stock without stockholder approval could have the effect of delaying, deferring or preventing a change of control of us or the removal of existing management. We have no preferred stock outstanding at the date hereof. Although we do not currently intend to issue any shares of preferred stock, we cannot assure you that we will not do so in the future.

Dividends

We have not paid any cash dividends on our common stock to date. The payment of cash dividends in the future will be dependent upon our revenues and earnings, if any, capital requirements and general financial conditions. The payment of any cash dividends is within the discretion of our board of directors at such time. Further, if we incur any indebtedness, our ability to declare dividends may be limited by restrictive covenants we may agree to in connection therewith.

Transfer Agent for our Common Stock

The transfer agent for our common stock is Continental Stock Transfer & Trust Company. We have agreed to indemnify Continental Stock Transfer & Trust Company in its roles as transfer agent, its agents and each of its stockholders, directors, officers and employees against all claims and losses that may arise out of acts performed or omitted for its activities in that capacity, except for any liability due to any gross negligence, willful misconduct or bad faith of the indemnified person or entity.

Certain Anti-Takeover Provisions of Delaware Law and our Second Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws

We are subject to the provisions of Section 203 of the DGCL regulating corporate takeovers. This statute prevents certain Delaware corporations, under certain circumstances, from engaging in a “business combination” with:

A “business combination” includes a merger or sale of more than 10% of our assets. However, the above provisions of Section 203 do not apply if:

The second amended and restated certificate of incorporation provides that our board of directors is classified into three classes of directors. As a result, in most circumstances, a person can gain control of our board only by successfully engaging in a proxy contest at two or more annual meetings.

Our authorized but unissued common stock and preferred stock are available for future issuances without stockholder approval (including a specified future issuance) and could be utilized for a variety of corporate purposes, including future offerings to raise additional capital, acquisitions and employee benefit plans. The existence of authorized but unissued and unreserved common stock and preferred stock could render more difficult or discourage an attempt to obtain control of us by means of a proxy contest, tender offer, merger or otherwise.

Exclusive forum for certain lawsuits

The second amended and restated certificate of incorporation requires, to the fullest extent permitted by law, that derivative actions brought in our name, actions against directors, officers and employees for breach of fiduciary duty and other similar actions may be brought only in the Court of Chancery in the State of Delaware and, if brought outside of Delaware, the stockholder bringing the suit will be deemed to have consented to service of process on such stockholder’s counsel. Although we believe this provision benefits us by providing increased consistency in the application of Delaware law in the types of lawsuits to which it applies, the provision may have the effect of discouraging lawsuits against our directors and officers.

Special meeting of stockholders

Our second amended and restated bylaws provide that special meetings of our stockholders may be called only by a majority vote of our board of directors, by our Chief Executive Officer or by our Chairman.

Advance notice requirements for stockholder proposals and director nominations

Our amended and restated bylaws provide that stockholders seeking to bring business before our annual meeting of stockholders, or to nominate candidates for election as directors at our annual meeting of stockholders, must provide timely notice of their intent in writing. To be timely, a stockholder’s notice will need to be received by the company secretary at our principal executive offices not later than the close of business on the 90th day nor earlier than the opening of business on the 120th day prior to the anniversary date of the immediately preceding annual meeting of stockholders. Pursuant to Rule 14a-8 of the Exchange Act, proposals seeking inclusion in our annual proxy statement must comply with the notice periods contained therein. Our amended and restated bylaws also specify certain requirements as to the form and content of a stockholders’ meeting. These provisions may preclude our stockholders from bringing matters before our annual meeting of stockholders or from making nominations for directors at our annual meeting of stockholders.

Action by written consent

Any action required or permitted to be taken by our common stockholders must be effected by a duly called annual or special meeting of such stockholders and may not be effected by written consent of the stockholders.

Classified Board of Directors

Our board of directors is divided into three classes, Class I, Class II and Class III, with members of each class serving staggered three-year terms. The second amended and restated certificate of incorporation provides that the authorized number of directors may be changed only by resolution of the board of directors. Subject to the terms of any preferred stock, any or all of the directors may be removed from office at any time, but only for cause and only by the affirmative vote of holders of a majority of the voting power of all then outstanding shares of our capital stock entitled to vote generally in the election of directors, voting together as a single class. Any vacancy on our board of directors, including a vacancy resulting from an enlargement of our board of directors, may be filled only by vote of a majority of our directors then in office.

Stock Exchange Listing

Our Common Stock and Public Warrants are listed on Nasdaq under the symbols “ADN” and “ADNWW”, respectively.

DESCRIPTION OF DEBT SECURITIES

The following description, together with the additional information we include in any applicable prospectus supplement, summarizes certain general terms and provisions of the debt securities that we may offer in one or more series under this prospectus. When we offer to sell a particular series of debt securities, we will describe the specific terms of the series in a supplement to this prospectus. We will also indicate in the supplement to what extent the general terms and provisions described in this prospectus apply to a particular series of debt securities. To the extent the information contained in the prospectus supplement differs from this summary description, you should rely on the information in the prospectus supplement.

We will issue any senior debt securities under the senior indenture that we will enter into with the trustee to be named in the senior indenture. We will issue any subordinated debt securities under the subordinated indenture that we will enter into with the trustee to be named in the subordinated indenture. We have filed forms of these indentures as exhibits to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC. Unless the context requires otherwise, we use the term “indenture” to refer to both the senior indenture and the subordinated indenture, as well as to refer to any supplemental indentures that specify the terms of a particular series of debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We use the term “trustee” to refer to either the senior trustee or the subordinated trustee, as applicable.

The following summary of material provisions of the senior debt securities, the subordinated debt securities, and the indenture is subject to, and is qualified in its entirety by reference to, all the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplement related to the debt securities that we sell under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the aggregate principal amount of debt securities that may be issued thereunder. The debt securities may be issued from time to time in one or more series and the terms of each series of debt securities will be established by or pursuant to a resolution of our board of directors and set forth in an officer’s certificate or a supplemental indenture. The particular terms of each series of debt securities will be described in a prospectus supplement relating to that series (including any pricing supplement or term sheet), including the following terms, if applicable:

In addition, we will provide you with information on the federal income tax considerations and other special considerations applicable to any of these debt securities in the applicable prospectus supplement.

If we denominate the purchase price of any of the debt securities in a foreign currency or currencies or a foreign currency unit or units, or if the principal of, or any premium or interest on, any series of debt securities is payable in a foreign currency or currencies or a foreign currency unit or units, we will provide you with information on the restrictions, elections, general tax considerations, specific terms, and other information with respect to that issue of debt securities and the foreign currency or currencies or foreign currency unit or units in the applicable prospectus supplement.

Transfer and Exchange

Each debt security will be represented by either one or more global securities registered in the name of The Depository Trust Company, as the depositary, or a nominee of the depositary (we will refer to any such debt security as a “global debt security”), or a certificate issued in definitive registered form (we will refer to any debt security represented by a certificate as a “certificated debt security”) as set forth in the applicable prospectus supplement. Except as set forth below, global debt securities will not be issuable in certificated form.

Certificated Debt Securities. You may transfer or exchange certificated debt securities at any office we maintain for this purpose in accordance with the terms of the indenture. No service charge will be made for any transfer or exchange of certificated debt securities, but we may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection with a transfer or exchange.

You may effect the transfer of certificated debt securities and the right to receive the principal of and any premium and interest on certificated debt securities only by surrendering the certificate representing those certificated debt securities and either reissuance by us or the trustee of the certificate to the new holder or the issuance by us or the trustee of a new certificate to the new holder.

Global Debt Securities and Book-Entry System. Each global debt security will be deposited with, or on behalf of, the depositary, and registered in the name of the depositary or a nominee of the depositary. Beneficial interests in global debt securities will not be issuable in certificated form unless (i) the depositary has notified us that it is unwilling or unable to continue as depositary for that global debt security or has ceased to be qualified to act as such as required by the indenture and we fail to appoint a successor depositary within 90 days of such event; (ii) we determine, in our sole discretion, not to have those securities represented by one or more global securities; or (iii) any other circumstances shall exist, in addition to or in lieu of those described above, as may be described in the applicable prospectus supplement. Unless and until a global debt security is exchanged for certificated debt securities under the limited circumstances described in the previous sentence, a global debt security may not be transferred except as a whole by the depositary to its nominee or by the nominee to the depositary, or by the depositary or its nominee to a successor depositary or to a nominee of the successor depositary.

Consolidation, Merger, and Sale of Assets

The indenture generally provides that we may not consolidate with or merge with or into, sell, convey, transfer, or dispose of all or substantially all of our assets to another entity, whether in one transaction or a series of related transactions, unless: (a)(i) the Company is the surviving corporation or (ii) the successor person (if other than the Company) (A) is a corporation, limited liability corporation, partnership, or trust organized under the laws of the United States, any state thereof, or the District of Columbia, and (B) expressly assumes by a supplemental indenture all of our obligations under the debt securities and the indenture, and (b) immediately after giving effect to the transaction no default or Event of Default (as defined below) and no circumstances which, after notice or lapse of time or both, would become an Event of Default, shall have happened and be continuing, and (c) we shall have delivered to the trustee an officer’s certificate and an opinion of counsel, each stating that such consolidation, merger, or transfer and such supplemental indenture comply with the indenture.

Notwithstanding the above, (i) any subsidiary of the Company may consolidate with, merge into, or transfer all or part of its properties to us and (ii) the Company may merge with or into an affiliate of the Company incorporated or formed solely for the purpose of reincorporating or reorganizing the Company in another state of the United States or the District of Columbia or changing the legal domicile of the Company or for the sole purpose of forming or collapsing a holding company structure or changing the form of legal entity. Neither an officer’s certificate nor an opinion of counsel shall be required to be delivered in connection therewith.

Events of Default

“Event of Default” means, with respect to any series of debt securities, any of the following:

No Event of Default with respect to a particular series of debt securities (except as to certain events of bankruptcy, insolvency, or reorganization) necessarily constitutes an Event of Default with respect to any other series of debt securities. The occurrence of certain Events of Default or an acceleration under the indenture may constitute an Event of Default under certain indebtedness of ours or our subsidiaries outstanding from time to time.

If an Event of Default with respect to any series of debt securities at the time outstanding occurs and is continuing (other than an Event of Default resulting from certain events of bankruptcy, insolvency, or reorganization), then the trustee or the holders of not less than 25% in principal amount of the outstanding debt securities of that series may, by a notice in writing to us (and to the trustee if given by the holders), declare to be due and payable immediately the principal of (or, if the debt securities of that series are discount securities, that portion of the principal amount as may be specified in the terms of that series) and accrued and unpaid interest, if any, on all debt securities of that series. In the case of an Event of Default resulting from certain events of bankruptcy, insolvency, or reorganization, the principal amount (or such specified amount) of and accrued and unpaid interest, if any, on all outstanding debt securities will become and be immediately due and payable without any declaration or other act on the part of the trustee or any holder of outstanding debt securities. At any time after a declaration of acceleration with respect to debt securities of any series has been made, but before a judgment or decree for payment of the money due has been obtained by the trustee, the holders of a majority in principal amount of the outstanding debt securities of that series, by written notice to us and the trustee, may rescind and annul such declaration of acceleration and its consequences if all Events of Default, other than the non-payment of accelerated principal and interest, if any, with respect to debt securities of that series, have been cured or waived as provided in the indenture. We refer you to the prospectus supplement relating to any series of debt securities that are discount securities for the particular provisions relating to acceleration of a portion of the principal amount of those discount securities upon the occurrence of an Event of Default.

The indenture provides that the trustee will be under no obligation to perform any duty or exercise any of its rights or powers under the indenture unless the trustee receives indemnity satisfactory to it against any cost, liability, or expense, which might be incurred by it in performing that duty or exercising that right or power. Subject to certain rights of the trustee, the holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method, and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to the debt securities of that series.

No holder of any debt security of any series will have any right to institute any proceeding, judicial or otherwise, with respect to the indenture or for the appointment of a receiver or trustee, or for any remedy under the indenture, unless:

Notwithstanding any other provision in the indenture, the holder of any debt security will have an absolute and unconditional right to receive payment of the principal of, and any interest on, that debt security on or after the due dates expressed in that debt security (or, in the case of redemption, on the redemption date, subject to the satisfaction of any conditions to such redemption) and to institute suit for the enforcement of any such payment, and such rights shall not be impaired without the consent of such holder.

The indenture requires us, within 120 days after the end of our fiscal year, to furnish to the trustee a statement as to compliance with the indenture from our principal executive officer, principal financial officer, or principal accounting officer. If a default or Event of Default occurs and is continuing with respect to the debt securities of any series and if it is actually known to a responsible officer of the trustee, the trustee shall mail to each holder of the debt securities of that series notice of a default or Event of Default within 90 days after it occurs or, if later, after a responsible officer of the trustee has knowledge of such default or Event of Default. The indenture provides that the trustee may withhold notice to the holders of debt securities of any series of any default or Event of Default (except in payment on any debt securities of that series) with respect to debt securities of that series if the trustee determines in good faith that withholding notice is in the interest of the holders of those debt securities.

Modification and Waiver

We and the trustee may modify and amend or supplement the indenture or the debt securities of one or more series without the consent of any holder of any debt security:

We may also modify and amend the indenture with the consent of the holders of at least a majority in principal amount of the outstanding debt securities of each series affected by the modifications or amendments. We may not make any modification or amendment without the consent of the holders of each affected debt security then outstanding if that amendment will:

Except for certain specified provisions, the holders of at least a majority in principal amount of the outstanding debt securities of any series may, on behalf of the holders of all debt securities of that series, by written notice to the trustee, waive our compliance with provisions of the indenture or the debt securities with respect to that series. The holders of a majority in principal amount of the outstanding debt securities of any series may, on behalf of the holders of all the debt securities of that series, waive any past default under the indenture with respect to that series and its consequences, except a default in the payment of the principal of, or any interest on, any debt security of that series; provided, however, that the holders of a majority in principal amount of the outstanding debt securities of any series may rescind an acceleration and its consequences, including any related payment default that resulted from the acceleration.

Satisfaction and Discharge of Indenture

The indenture shall cease to be of further effect with respect to a series of debt securities when either:

In each case, we will also pay all other sums payable by us under the indenture with respect to the debt securities of that series and deliver to the trustee an opinion of counsel and an officer’s certificate, each stating that all conditions precedent to satisfaction and discharge with respect to the debt securities of that series have been complied with.

Defeasance

Legal Defeasance. The indenture provides that, unless otherwise provided by the terms of the applicable series of debt securities, we may be discharged from any and all obligations in respect of the debt securities of any series (subject to certain exceptions). We will be so discharged upon the deposit with the trustee, in trust, of money and/or U.S. government obligations or, in the case of debt securities denominated in a single currency other than U.S. dollars, government obligations of the government that issued or caused to be issued such currency, that, through the payment of interest and principal in accordance with their terms, will provide money in an amount sufficient in the opinion of a nationally recognized firm of independent public accountants or investment bank to pay and discharge each installment of principal of and interest, if any, on and any mandatory sinking fund payments in respect of the debt securities of that series on the stated maturity of those payments in accordance with the terms of the indenture and those debt securities.

This discharge may occur only if, among other things, we have delivered to the trustee an opinion of counsel stating that we have received from, or there has been published by, the U.S. Internal Revenue Service a ruling or, since the date of execution of the indenture, there has been a change in the applicable U.S. federal income tax law, in either case to the effect that, and based thereon such opinion shall confirm that, the holders of the debt securities of that series will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the deposit, defeasance and discharge and will be subject to U.S. federal income tax on the same amounts and in the same manner and at the same times as would have been the case if the deposit, defeasance, and discharge had not occurred.

Defeasance of Certain Covenants. The indenture provides that, unless otherwise provided by the terms of the applicable series of debt securities, upon compliance with certain conditions, which we refer to as covenant defeasance, then:

The conditions include:

Governing Law

The indenture and any debt securities issued thereunder will be governed by and construed in accordance with the laws of the State of New York (without regard to the conflicts of law provisions other than Section 5-1401 of the New York General Obligations Law).

Subordination of Subordinated Debt Securities

The subordinated debt securities will be subordinate and junior in priority to certain of our other indebtedness to the extent described in a prospectus supplement.

DESCRIPTION OF WARRANTS

We may issue warrants to purchase shares of our common stock, shares of our preferred stock, or debt securities. We may issue warrants independently of or together with shares of our common stock, shares of our preferred stock, debt securities, or other securities offered by any prospectus supplement. Warrants sold with other securities may be attached to or separate from shares of our common stock, shares of our preferred stock, debt securities, or other securities. We may issue warrants under one or more warrant agreements between us and a bank or trust company, as warrant agent, which we will name in the prospectus supplement relating to the particular issue of offered warrants. If we appoint a warrant agent, such warrant agent will act solely as our agent in connection with the warrants and will not assume any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants.

The prospectus supplement relating to any warrants we offer will include specific terms relating to the offering. These terms may include some or all of the following:

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. Holders of the warrants may exercise the warrants at any time up to the specified time on the expiration date that we set forth in the applicable prospectus supplement. After the specified time on the expiration date, unexercised warrants will become void.

Warrants may be exercised as described in the applicable prospectus supplement. Upon receipt of the required payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will, as soon as practicable, issue and deliver the underlying securities purchasable upon such exercise. If fewer than all of the warrants represented by a warrant certificate are exercised, we will issue a new warrant certificate for the remaining amount of warrants.

The description in the applicable prospectus supplement of any warrants we offer will not necessarily be complete and will be qualified in its entirety by reference to the applicable form of warrant agreement, including a form of warrant certificate, which will describe the terms of the series of warrants being offered, and which will be filed with the SEC and incorporated by reference in the registration statement of which this prospectus is a part.

DESCRIPTION OF RIGHTS

We may issue rights for the purchase of shares of our common stock, shares of our preferred stock, or debt securities. Each series of rights will be issued under a separate rights agreement to be entered into with a bank or trust company, as rights agent, all as set forth in the applicable prospectus supplement. The rights agent will act solely as our agent in connection with the certificates relating to the rights and will not assume any obligation or relationship of agency or trust with any holders of rights certificates or beneficial owners of rights.

The prospectus supplement relating to any rights we offer will describe the specific terms of those rights. These terms may include some or all of the following:

The description in the applicable prospectus supplement of any rights we offer will not necessarily be complete and will be qualified in its entirety by reference to the applicable form of rights agreement, which will describe the terms of the series of rights being offered, and which will be filed with the SEC and incorporated by reference in the registration statement of which this prospectus is a part.

DESCRIPTION OF UNITS

We may issue units comprising two or more securities described in this prospectus in any combination. For example, we might issue units consisting of a combination of debt securities and warrants to purchase common stock. The following description sets forth certain general terms and provisions of the units that we may offer pursuant to this prospectus. The particular terms of the units and the extent, if any, to which the general terms and provisions may apply to the units so offered will be described in the applicable prospectus supplement.

Each unit will be issued so that the holder of the unit also is the holder of each security included in the unit. Thus, the unit will have the rights and obligations of a holder of each included security. Units will be issued pursuant to the terms of a unit agreement, which may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date.

The prospectus supplement relating to any particular issuance of units we offer will describe the terms of those units. These terms may include some or all of the following:

The description in the applicable prospectus supplement of any units we offer will not necessarily be complete. Such description will be qualified in its entirety by reference to the applicable form of unit agreement, including a form of unit certificate, which will describe the terms of the series of units being offered, and which will be filed with the SEC and incorporated by reference in the registration statement of which this prospectus is a part.

PLAN OF DISTRIBUTION

We may offer and sell the securities described in this prospectus from time to time in one or more transactions, including without limitation:

In addition, the manner in which we may offer and sell some or all of the securities described in this prospectus includes, without limitation, through:

A prospectus supplement with respect to each offering of securities will set forth the terms of the offering and the method of distribution of the securities and will identify any firms acting as underwriters, dealers or agents in connection with the offering, including:

The offer and sale of the securities described in this prospectus by us, the underwriters or the third parties described above may be effected from time to time in one or more transactions, including privately negotiated transactions, either:

In connection with the sale of the securities, underwriters, dealers, or agents may be deemed to have received compensation from us in the form of underwriting discounts or commissions and also may receive commissions from securities purchasers for whom they may act as agent. Underwriters may sell the securities to or through dealers, and the dealers may receive compensation in the form of discounts, concessions, or commissions from the underwriters or commissions from the purchasers for whom they may act as agent.

Underwriters, dealers, and agents participating in the securities distribution may be deemed to be underwriters, and any discounts and commissions they receive and any profit they realize on the resale of the securities may be deemed to be underwriting discounts and commissions under the Securities Act. Underwriters and their controlling persons, dealers, and agents may be entitled, under agreements entered into with us, to indemnification against and contribution toward specific civil liabilities, including liabilities under the Securities Act.

Any securities we sell pursuant to a prospectus supplement may or may not be listed on a national securities exchange. It is possible that one or more underwriters may make a market in the securities, but such underwriters will not be obligated to do so and may discontinue any market making at any time without notice. No assurance can be given as to the liquidity of, or the trading market for, any offered securities.

In connection with any offering, the underwriters may purchase and sell securities in the open market. These transactions may include short sales, stabilizing transactions, and purchases to cover positions created by short sales. Short sales involve the sale by the underwriters of a greater number of securities than they are required to purchase in an offering. Stabilizing transactions consist of bids or purchases made for the purpose of preventing a decline in the market price of the securities while an offering is in progress. The underwriters also may impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the underwriters have repurchased securities sold by or for the account of that underwriter in stabilizing or short-covering transactions. These activities by the underwriters may stabilize, maintain, or otherwise affect the market price of the securities. As a result, the price of the securities may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued by the underwriters at any time. Underwriters may engage in over-allotment. If any underwriters create a short position in the securities in an offering in which they sell more securities than are set forth on the cover page of the applicable prospectus supplement, the underwriters may reduce that short position by purchasing the securities in the open market.

Underwriters, dealers, or agents that participate in the offer of securities, or their affiliates or associates, may have engaged or engage in transactions with and perform services for, us or our affiliates in the ordinary course of business for which they may have received or receive customary fees and reimbursement of expenses.

LEGAL MATTERS

Unless otherwise indicated in the applicable prospectus supplement, certain legal matters regarding the validity of the securities to be offered by this prospectus will be passed upon for us by Manatt, Phelps & Phillips, LLP, Los Angeles, California. Additional legal matters may be passed upon for us or any underwriters, dealers, or agents by counsel that will be named in the applicable prospectus supplement.

EXPERTS

The consolidated financial statements of Advent Technologies Holdings, Inc. appearing in Advent Technologies Holdings, Inc.'s Annual Report (Form 10-K) for the year ended December 31, 2022, have been audited by Ernst & Young (Hellas) Certified Auditors Accountants S.A., independent registered public accounting firm, as set forth in their report thereon, (which contains an explanatory paragraph describing conditions that raise substantial doubt about the Company’s ability to continue as a going concern as described in Note 1 to the consolidated financial statements), included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing. Ernst & Young (Hellas) Certified Auditors Accountants S.A. is located at Chimarras 8B, 15125, Maroussi, Athens, Greece and is registered as a corporate body with the public register for company auditors-accountants kept with the Body of Certified Auditors-Accountants, or SOEL, Greece with registration number 107.

ADVENT TECHNOLOGIES HOLDINGS, INC.

$200,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Rights

Units

PROSPECTUS

May 2, 2023