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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10–K

For the fiscal year ended December 31, 2005

OR

For the transition period from                      to                     

Commission File No. 000-49604

(Exact name of registrant as specified in its charter)

12015 Lee Jackson Highway, Fairfax, VA 22033

(Address of principal executive offices)

(703) 218-6000

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act:

Class A Common Stock, Par Value $0.01 Per Share

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ¨    No  x

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act.    Yes  ¨    No  x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

The aggregate market value of the voting stock held by non-affiliates of the registrant as of June 30, 2005 was $552,757,154 (based on the closing price of $31.04 per share on June 30, 2005, as reported by the Nasdaq National Market).

There were the following numbers of shares outstanding of each of the registrant’s classes of common stock as of February 28, 2006: ManTech International Corp. Class A Common Stock, $.01 par value per share, 18,028,522 shares; ManTech International Corp. Class B Common Stock, $.01 par value per share, 15,065,093 shares.

DOCUMENTS INCORPORATED BY REFERENCE

Certain portions of the definitive Proxy Statement to be filed with the Securities Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2006 Annual Meeting of Stockholders, to be filed subsequent to the date hereof, are incorporated by reference into Part III (Items 10, 11, 12, 13 and 14) of this Annual Report on Form 10-K. Such definitive Proxy Statement will be filed with the Commission not later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K.

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PART I

Item 1. Business

This Annual Report on Form 10-K contains forward-looking statements that involve substantial risks and uncertainties, many of which are outside of our control. We believe that these statements are within the definition of the Private Securities Litigation Reform Act of 1995. You can often identify these statements by the use of words such as “may,” “will,” “expect,” “intend,” “anticipate,” “believe,” “plan,” “seek,” “estimate,” “continue” and other similar words or variations on such words. Additionally, statements concerning future matters or matters that are not historical are forward-looking statements. You should read our forward-looking statements carefully because they discuss our future expectations, make projections of our future results of operations or financial condition, or state other “forward-looking” information.

Although forward-looking statements in this Annual Report reflect the good faith judgment of management, such statements can only be based on facts and factors currently known by us. Consequently, forward-looking statements are inherently subject to risks and uncertainties and actual results and outcomes may differ materially from the results and outcomes discussed in or anticipated by the forward-looking statements. We believe that it is important to communicate our future expectations to our investors. However, there may be events in the future that we are not able to predict accurately or control. The factors that could cause or contribute to such differences include, but are not limited to, those discussed in Item 1A “Risk Factors” below, as well as those discussed elsewhere in this Annual Report. We urge you not to place undue reliance on these forward-looking statements, which speak only as of the date of this Annual Report. We undertake no obligation to revise or update any forward-looking statements in order to reflect any event or circumstance that may arise after the date of this Annual Report. We also suggest that you carefully review and consider the various disclosures made in this Annual Report that attempt to advise interested parties of the risks and factors that may affect our business, financial condition, results of operations and prospects.

In this document, unless the context indicates otherwise, the terms “Company” and “ManTech,” as well as the words “we,” “our,” “ours” and “us,” refer to both ManTech International Corporation and its consolidated subsidiaries. The term “registrant” refers only to ManTech International Corporation, a Delaware corporation that is the successor by merger to ManTech International Corporation, a New Jersey corporation. As a result of the merger, in January 2002, we reincorporated from New Jersey to Delaware.

Business Overview

ManTech is a leading provider of innovative technologies and solutions for mission-critical national security programs for the Intelligence Community, the Departments of Defense, State, Homeland Security, and Justice, and other U.S. federal government agencies. Our expertise includes engineering, systems integration, software services, enterprise architecture, information assurance and security architecture, intelligence operations and analysis support, network and critical infrastructure protection, information operations and computer forensics, information technology, communications integration and engineering support. With approximately 6,000 highly qualified employees, we operate in the United States and over 40 countries worldwide.

In 2005, we had revenues of $980.3 million, an 18.5% increase over our 2004 revenue of $826.9 million. We have grown substantially in the last four years, from revenues of $431.4 million at the end of 2001, just prior to our initial public offering (IPO) in February 2002, to our current levels today. We derive a substantial majority of our revenues from our customers in the Intelligence Community and the Department of Defense:

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Our Intelligence Community and Department of Defense customers include the Office of the Secretary of Defense, the Department of State, the Department of Homeland Security, various intelligence agencies, joint intelligence task forces, the U.S. Army, Navy, Air Force and Marine Corps and joint military commands. We also provide solutions to federal government civilian agencies, including the Department of Justice, NASA, and EPA, as well as to state and local governments and commercial customers.

Industry Background

The federal government is the largest consumer of information technology services and solutions in the United States. We believe that the federal government’s spending on information technology will continue to increase in the next several years, driven by the expansion of national defense and homeland security programs, the continued need for sophisticated intelligence gathering and information sharing, increased reliance on technology service providers, due to shrinking ranks of government employee technical professionals, and the continuing impact of federal procurement reform and Office of Management and Budget mandates regarding IT spending. Federal government spending on information technology has consistently increased in each year since 1980. Input, an independent federal government market research firm, expects this trend to continue, with federal government spending on information technology forecast to increase from $59.2 billion in federal fiscal year 2005 to $78.8 billion in federal fiscal year 2010, representing an annual growth rate of 5.9%. Moreover, this data may not fully reflect government spending on classified intelligence programs, operational support services to our armed forces and complementary technical services, which include sophisticated systems engineering.

Across the National Security community, we see the following trends that will continue to drive increased spending and dependence on technology support contractors.

Increased Spending on Network Centric Warfare and Support to the Warfighter. The Department of Defense is the largest purchaser of information technology in the federal government. For fiscal year 2006, the President has signed a bill that authorizes $410.8 billion in defense spending. This same appropriations bill includes supplemental funding of $55.8 billion to the Department of Defense, with the President preparing an additional request of $70 billion to provide funding for the Global War on Terror and operations in Iraq and Afghanistan. For fiscal year 2007, the President has requested a budget of $439.3 billion, a 6.9% increase from fiscal year 2006, excluding supplementals generally used to support current ongoing operational efforts and the Global War on Terror.

In addition to the recent budget request, the Department of Defense recently completed its Quadrennial Defense Review (QDR), which is published every four years, and provides the Department of Defense’s plans for future strategic direction, including procurement trends. According to a Department of Defense QDR summary, the QDR is aimed at emphasizing agility, flexibility, speed, responsiveness and pre-emptive military concepts, which all rely on information technology systems. The 2006 QDR also emphasizes the increasing importance of net-centric warfare, which involves enabling critical relationships between organizations and people to accelerate the speed of business processes, operational decision-making and subsequent actions. According to the QDR, net-centricity requires viewing information as an enterprise asset to be shared and as a weapon system to be protected. Finally, the QDR introduced the concept of the 21^st Century Total Force, which explicitly highlights the contractor’s role in support of the Department of Defense in an integrated long-term context.

Increased Spending on Intelligence Gathering and Information Sharing. The terrorist attacks of September 11, 2001 and subsequent events (especially the asymmetric warfare being waged in the Global War on Terror) have intensified the federal government’s commitment to strengthen our country’s military, intelligence, and homeland security capabilities and increased the need for information technology capable of supporting these functions. We believe intelligence agencies will increase demand for data and text mining solutions to enable them to extract, analyze, and present data gathered from the massive volumes of information available through open sources such as the Internet. This increased focus on national security, homeland security, and intelligence has also reinforced the need for interoperability among the many disparate information technology systems

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throughout the federal government. We believe the Department of Homeland Security and the intelligence agencies are increasingly interested in enterprise systems that enable better coordination and communication within and among agencies and departments.

Increasing Reliance on Technology Service Providers. The demand for technology service providers is expected to increase due to the need for federal agencies to maintain core operational functions while the available technical workforce shrinks. The National Academy of Public Administrators estimates that approximately 50.0% of the federal government information technology workforce are near eligibility to retire and that there will be a shortage of technically-skilled replacements. Given the difficulty the federal government has experienced in hiring and retaining skilled technology personnel in recent years, we believe the federal government will need to rely heavily on technology service providers that have experience with government legacy systems, can sustain mission-critical operations and have the required government security clearances to deploy qualified personnel in classified environments.

Continuing Impact of Federal Procurement Reform. In recent years, federal agencies have had increased access to alternative choices in their contract acquisition vehicles—such as indefinite delivery/indefinite quantity contracts (ID/IQs), Government Wide Acquisition Contracts (GWACs), the General Services Administration (GSA) schedule and agency specific Blanket Purchase Agreements (BPAs). These choices have created a market-based environment in government procurement. The environment has increased contracting flexibility and provides government entities access to multiple channels to contractor services. Contractors’ successful past performance, as well as technical capabilities and management skills, remain critical elements of the award process. We believe the increased flexibility associated with the multiple channel access, such as ID/IQs, GWACs, GSA schedule contracts and BPAs, will result in the continued utilization of these contracting vehicles in the future, and will facilitate access to service providers to meet the increased demand for, and delivery of, required services and solutions.

Our Solutions and Services

We deliver comprehensive information technology, technical and other services and solutions for mission-critical, enterprise information technology and communication systems, primarily in support of National Security programs for the Intelligence Community and Department of Defense. Our solutions include the following services offerings, often delivered in combination over an extended period of time in support of long-term programs:

Our offerings fall into one or more of three basic categories: Secure Systems and Infrastructure; Information Technology; and Systems Engineering.

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Secure Systems and Infrastructure Solutions

We provide a broad range of solutions to enhance systems and network availability and mission-critical performance of our customers’ hardware, software, computer network and telecommunication assets and operations, including the following.

Intelligence Operations and Analysis Support. We provide services for strategic and tactical intelligence systems, networks and facilities in support of the Intelligence Community and Department of Defense. To support classified systems and facilities designed to collect, analyze, process and report on various intelligence sources, we develop and integrate collection and analysis systems and techniques. Our intelligence-related services also include the design, rapid development and prototyping, integration and management of real-time signal processing systems. We also provide support to the development and application of analytical techniques to counter-terrorist operations. Our offerings also include the provision of subject matter expert analysts who work directly with the Intelligence Community and Department of Defense customers to produce long-term classified and unclassified research/analytic reporting, as well as provide real-time analytic support for ongoing intelligence operations.

Secrecy Management and Program Security Architecture. We provide secrecy management and security infrastructure services for highly classified programs, including intelligence operations and military programs. Due to the highly sensitive and classified nature of these programs, opportunities are often limited to a select number of providers that possess the requisite capabilities, qualifications and special access clearances. We provide secrecy and security services including vulnerability assessment, exposure analysis, secrecy architecture design, security policy development and implementation, lifecycle acquisition program security, system security engineering, security awareness and training, comprehensive security support services, and technical certification and accreditation services.

For example, we provide integrated security support for the Joint Strike Fighter (JSF) Program. With numerous highly classified technologies incorporated in its design and international content in both its development and its usage, the JSF Program presents the most complex security problem set of any weapon system in our nation’s history. We provide a complete range of integrated security services to the JSF Program Office, including physical, personnel, and cyber security disciplines, as well as in-depth support to international disclosure controls. Our established performance in security architecture development and critical information protection, and our security and risk management methodologies, establish a framework for lifecycle JSF program protection that encompasses all security disciplines.

Information Assurance. We provide comprehensive lifecycle information assurance/security support services to the Department of State, the Department of Justice and agencies in the Intelligence Community. Our services include around the clock intrusion detection and network monitoring, cyber security incident response, network security design, architecture and engineering, certification and accreditation, information assurance training and awareness support, policy review and reporting, compliance auditing, and cyber threat analysis and vulnerability analysis. In 2005, our State Department customer, which supports a 50,000 user population operating in 260 locations worldwide on classified and unclassified networks, was awarded the prestigious National Security Agency sponsored Frank R. Rowlett Award for excellence in information assurance for efforts directly supported by our personnel.

Communication Systems and Infrastructure Support. We design, develop, modify and maintain secure communication systems and network infrastructures. This process involves evaluating industry standards, systems architectures and applications in order to recommend and develop technology solutions and integrate them into a customer’s secure communication systems. We also procure, install and test new voice, data and video communication systems.

For example, we operate regional support centers in the United States, Iraq, Afghanistan, Germany, Korea, Kuwait, Bosnia and elsewhere for intelligence, electronic warfare and related critical missions. We perform

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systems and network troubleshooting, maintenance, repair and installation, as well as integration and testing of electronic, electrical and mechanical equipment designed for vehicular, airborne and portable platforms. Our personnel stationed at these regional support centers have supported every major military deployment since 1990. Beginning with Desert Storm and currently for Iraqi Freedom, our personnel have provided Command, Control, Communications, Computers and Intelligence (C4I) systems operations and maintenance support to deployed units in hostile environments. As part of other overseas activities, we have personnel deployed at locations in Afghanistan, and Kyrgyzstan in support of Air Force operations.

Information Technology Solutions

We provide a broad range of information technology solutions to our customers, including the following.

Enterprise Systems Engineering. We provide network architecture planning and implementation services and systems engineering services in support of enterprise-wide network infrastructures and components that include LAN/WAN architectures, messaging architectures, network management solutions, directory services architecture, and web hosting. These services are provided within secure environments requiring the application of multi-level security policies across the enterprise. For example, we developed and implemented a scalable enterprise-wide network and messaging infrastructure accredited to meet Director of Central Intelligence Directive 6/3 for Protection Level 3 in support of an Intelligence Community customer. Additionally, we provide enterprise systems engineering services to include LAN/WAN, messaging, and e-mail infrastructure architecture and implementation to an Intelligence Community customer.

Information Operations. We provide customers in the Department of Defense and Intelligence Community a wide range of services in the areas of computer forensic analysis, cyber defense, intrusion operations, and network monitoring operations. We perform full-scope digital analysis including advanced data mining analysis, atypical data recovery techniques, and data extraction. We conduct advanced computer network operations analysis including the reverse engineering of network protocols, applications, and operating systems. We also provide custom internet enumeration and analysis services and full lifecycle support for internet access architectures.

For example, in support of a customer, we developed and staffed a national level computer forensic laboratory and provided a broad spectrum of subject matter expertise, including the following:

We played a crucial role in the successful establishment of a national level computer forensic laboratory and provided advanced forensics support.

Enterprise Application Solutions. We design, develop, implement, test, maintain and web-enable software applications for our customers’ information systems and network infrastructures. We provide comprehensive e-commerce services, including web development efforts that focus on designing and maintaining scalable, interoperable, reliable and portable end-to-end information management solutions. We apply these capabilities to critical customer missions requiring multi-layered security within the application in order to improve information sharing and collaboration.

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For example, we developed a state-of-the-art analytic environment that provides access to regional, national and international information with appropriate security level access controls providing direct operational support to time sensitive counterterrorism activities in support of an Intelligence Community customer.

We also developed the major portions of the Homeland Security Information Network (HSIN), which the Department of Homeland Security uses to allow all states, major urban areas, counties and certain foreign government allies to collect, share and disseminate information to combat terrorism. We based HSIN on the Joint Regional Information Exchange System (JRIES), a technology solution that we developed for the Defense Intelligence Agency. HSIN is a secure, around the clock, web-based, real-time collaborative tool that has interactive connectivity with the Department of Homeland Security operations center. This secure system significantly enhances the ability of users to exchange real-time threat information at the sensitive-but-unclassified level. In 2005, HSIN was utilized to support rescue and relief efforts in the aftermath of hurricane Katrina.

Systems/Network Maintenance Services. We have extensive experience in maintaining a wide range of information management resources for our customers. We perform comprehensive systems administration, including around the clock support for continuous mission operations. For example, for the Army, we provide systems administration and help desk functions at a domestic location for a command and management system, as well as help desk functions in an overseas remote location that supports 1,500 users. For this customer, we also provide on-site support for the command and management system workstations and networks located throughout countries in Central and South America.

Systems Engineering Solutions

We offer our customers a broad range of systems engineering solutions, including the following.

Systems Engineering Services. We perform comprehensive systems engineering services to analyze and develop solutions for customer hardware and software requirements. We also evaluate existing system designs to determine if performance enhancements or cost savings can be derived through the integration of current technologies. Since 1968, our engineers and scientists have been providing critical acoustic systems engineering support to the Navy that includes data acquisition and analysis, model instrumentation and maintenance, and program and logistics support. Our personnel have performed acoustic testing for every operational Navy combatant—both surface and submarine. Our support to the Navy also involves data acquisition and recording technology, advanced signal processing and sonar systems engineering analysis. We also support combat identification systems development, and provide systems engineering and technical services that support the design and installation of communication, intelligence, electronic warfare and information systems aboard Navy and Coast Guard ships and at shore-based facilities.

Testing and Evaluation. We test complex and mission-critical hardware and software systems used by the Army, Navy and NASA, with many of these customer relationships spanning more than three decades. We have played key roles in improving the performance, reliability, maintainability, supportability and weapons effectiveness of all Navy in-service rotary and fixed wing platforms, including the F/A-18E/F Super Hornet, and their associated ordnance. We are participating in the development of plans for testing and evaluating the Joint Strike Fighter and the Multi-Mission Maritime Aircraft.

We have supported the NASA Goddard Space Flight Center for more than 30 years as the principal contractor responsible for providing comprehensive integration, environmental test engineering and operations support for systems such as the Hubble Space Telescope. Our space payload test and integration services have supported every in-house earth orbit program since 1971. We conduct a broad range of tests, including structural, acoustics, vibration, space simulation and electromagnetic tests, to certify that all flight hardware can withstand the extreme conditions of space flight. We have been recognized within Goddard and the NASA community for our test, integration, transportation and launch site support.

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Independent Validation and Verification. We perform tests to certify that new systems or upgraded systems operate in accordance with their design requirements. For example, we have performed certification services for aircraft weapon systems in support of U.S. Naval Air Systems Command programs.

Our Growth Strategy

Our objective is to grow our business profitably as a premier provider of comprehensive information technology and technical services solutions to the federal government market. Our strategies for achieving this objective include the following.

Expand Our Customer Base. We intend to capitalize on our long-term relationships with our customers and our reputation within the Intelligence Community, Department of Defense and other government agencies to attract new customers and to cross-sell our broad array of solutions to our existing customers. Under the “best value” contracting process that has resulted from reforms in the government process, past performance and technical approach are key factors that the government may consider when evaluating competitive bids. Based on our long-term support to numerous customers, we believe we have a successful past performance track record and have demonstrated technical expertise that gives us credibility with these customers and enhances our ability to be successful in bidding on follow-on contracts and in competing for new programs of both existing and new customers. As customers seek a “single integrator solution” approach, we believe that we have sufficient experience and expertise to support such programs for current and new customers. Because our personnel are on-site with our customers or work in close proximity to our customers, we develop close relationships with them and are often able to enhance our customers’ operations by rapidly identifying and developing solutions for customer-specific requirements.

Target High Growth Segments of the Market. We believe the projected growth in government information technology and technical services spending will present opportunities for development and delivery of advanced technology solutions for enterprise applications and information systems. We intend to expand our service offerings in high growth program areas. In particular, we intend to focus on providing new or improved solutions in information assurance, including cyber security and homeland defense programs, and other secure systems and infrastructure solutions in support of National Security programs that support the Global War on Terror and ongoing operations in active theaters of military and intelligence operations, such as Iraq and Afghanistan. We also plan to continue to target customers seeking to improve their IT infrastructures and systems, especially those charged with building and operating enhanced web-based collaboration/sharing platforms. We have also identified information assurance and homeland defense programs as targeted growth areas.

Attract and Retain Highly Skilled and Highly Cleared Personnel. We intend to continue to attract and retain skilled professionals, including engineers, scientists, analysts, technicians and support specialists, to ensure that we have the capabilities to fulfill our customers’ requirements. We target candidates who have served in the military or as civilian experts in the Intelligence Community and Department of Defense, as well as those who are leading specialists in their technology disciplines. We believe we can continue to retain our employees by offering competitive compensation and incentive plans, opportunities for career growth through company-supported education programs and diverse, challenging assignments at over 180 locations worldwide. As of December 31, 2005, over 75% of our workforce possess clearances and over 50% possess Top Secret or above level clearances.

Leverage Intellectual Property to Provide Complete Technology Solutions. We intend to leverage our internally developed intellectual property to provide complete technology solutions and generate incremental revenue opportunities across our service offerings. For example, we have implemented our NetWitness product, our integrated network forensic solution, into several intelligence agencies where we previously provided only technology services.

Pursue Strategic Acquisitions. We plan to enhance our internal growth by selectively pursuing strategic acquisitions of businesses that can cost-effectively broaden our domain expertise and service offerings and allow us

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to establish relationships with new customers. We have acquired six companies since our IPO in February 2002, accelerating our overall revenue growth. We are focused primarily on acquiring businesses that provide value-added solutions for the Intelligence Community and Department of Defense, but we will also consider opportunities to acquire other businesses where we can leverage our reputation and experienced management team.

Our Customers

Our customers consist primarily of U.S. federal government intelligence, military and civilian agencies We have successful, long-standing relationships with our customers, having supported many of them for 15 to 30 years. Some of our representative customers include:

We derive the vast majority of our revenues from our federal government customers, consisting primarily of customers in the Intelligence Community and Department of Defense.

Our federal government customers typically exercise independent contracting authority, and multiple offices or divisions within an agency or department may directly, or through a prime contractor, use our services as a separate customer so long as that customer has independent decision-making and contracting authority within its organization. For example, under a blanket purchasing agreement with one of the Army’s contracting agencies, program managers throughout the Army and from other services and defense agencies are able to purchase a wide range of our solutions. One customer, the U.S. Army Lifecycle Management Command (LCMC-HQ) (formerly Communications-Electronic Command Headquarters—CECOM-HQ) accounted for 19.7% of our revenues for the year ended December 31, 2005, and 15.4% of our revenues for the year ended December 31, 2004. No single customer accounted for 10% or more of our revenues for the year ended December 31, 2003. In addition, there were no sales to any customers within a single country (except for the United States) where the sales accounted for 10% or more of our total revenue.

For 2005 and 2004, we derived 18.7% and 14.0%, respectively, of our revenues through relationships with prime contractors, who contract directly with the customer and subcontract to us.

Foreign Operations

We treat sales to U.S. government customers as sales within the United States, regardless of where services are performed. The percentages of total revenues by geographic customer for the last three years were as follows:

Other information relating to our foreign operations is provided in Note 4 to our consolidated financial statements.

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Backlog

At December 31, 2005, our backlog was $2.3 billion, of which $467 million was funded backlog. At December 31, 2004, our backlog was $1.6 billion, of which $444 million was funded backlog. Backlog and funded backlog represent estimates that we calculate on the basis described below. We expect that approximately 35% to 45% of our total backlog will be recognized as revenues prior to December 31, 2006.

We define backlog as our estimate of the remaining future revenues from existing signed contracts, assuming the exercise of all options relating to such contracts and including executed task orders issued under GSA schedule contracts. This includes an estimate of revenues for solutions that we believe we will be asked to provide in the future under the terms of executed multiple-award contracts for which we are not the sole provider, meaning that the customer could turn to other companies to fulfill the contract. It also includes an estimate of revenues from indefinite delivery, indefinite quantity contracts, which specify a maximum, but only a token minimum, amount of goods or services that may be provided under the contract. Backlog does not include the value for contracts where we have been given permission by the customer to begin or continue working, but where a formal contract or contract extension has not yet been signed.

We define funded backlog to be the portion of backlog for which funding currently is appropriated and allocated to the contract by the purchasing agency or otherwise authorized for payment by the customer upon completion of a specified portion of work. Our funded backlog does not include the full value of our contracts, because Congress often appropriates funds for a particular program or contract on a yearly or quarterly basis, even though the contract may call for performance that is expected to take a number of years.

Changes in the amount of our backlog and funded backlog result from potential future revenues from the execution of new contracts or the extension of existing contracts, reductions from contracts that end or are not renewed, reductions from the early termination of contracts, and adjustments to estimates for previously included contracts. Changes in the amount of our funded backlog also are affected by the funding cycles of the government. Our estimates of future revenues are necessarily inexact and the receipt and timing of any of these revenues is subject to various contingencies, many of which are beyond our control. The actual accrual of revenues on programs included in backlog and funded backlog may never occur or may change because a program schedule could change, a program could be canceled, a contract could be modified or canceled, an option that we have assumed would be exercised is not exercised, or initial estimates regarding the level of solutions that we may provide could prove to be wrong. For the same reason, we believe that period-to-period comparisons of backlog and funded backlog are not necessarily indicative of future revenues that we may receive.

Employees

As of December 31, 2005, we had approximately 6,000 employees, including approximately 300 part-time and temporary full-time employees. Over 700 employees were located outside of the United States.

Approximately 200 of our employees, all of whom are located at NASA’s Goddard Space Flight Center, are represented by the International Brotherhood of Electrical Workers union under a collective bargaining agreement. We have not experienced any work stoppage or strike by these employees and believe our relations with the union and our employees to be good.

Patents, Trademarks, Trade Secrets and Licenses

We own two patents in the United States and two patents in Canada. While we believe these patents are valid, we do not consider our business to be dependent on the protection of these patents in any material way.

We presently own 18 registered trademarks and service marks in the U.S., and we have three registered copyrights. Because most of our business involves providing services to federal government customers, our operations generally are not substantially dependent upon obtaining and/or maintaining copyright or trademark protections, although our operations make use of such protections.

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We license third party software, data and products. With the exception of our enterprise resource planning software, our operations are not materially dependent on such licenses.

We maintain a number of trade secrets that contribute to our success and competitive distinction and endeavor to accord such trade secrets protection adequate to ensure their continuing availability to us. While retaining protection of our trade secrets and vital confidential information is important, we are not materially dependent on maintenance of any specific trade secret or group of trade secrets.

We also enter into confidentiality and intellectual property agreements with our employees, which contain provisions that require them to disclose any inventions created during employment, convey all rights to inventions to us, and restrict the distribution of proprietary or confidential information.

Cyclicality

Expenditures by our customers tend to vary in cycles that reflect overall economic conditions and customer mission requirements, as well as budgeting and buying patterns. Our revenue has in the past been, and may in the future be, materially affected by a decline in the defense or other intelligence budgets or in the economy in general. Such future declines could alter our current or prospective customers’ spending priorities and budget cycles, or extend our sales cycle.

Competition

Our key competitors currently include divisions of large defense contractors such as BAE Systems, plc, Computer Sciences Corporation, General Dynamics, Lockheed Martin Corporation, Northrop Grumman Corporation, and Science Applications International Corporation, as well as a large number of smaller U.S. government contractors with specialized capabilities, such as CACI, Booz Allen & Hamilton and SRA International. Because of the diverse requirements of U.S. government customers and the highly competitive nature of large procurements, corporations frequently form teams to pursue contract opportunities. The same companies listed as competitors will, at times, team with us or subcontract to us in the pursuit of new business. We believe that the major competitive factors in our market are distinctive technical competencies, successful past contract performance, intelligence and military work experience, price of services, reputation for quality and key management with domain expertise.

2005 Acquisition

Gray Hawk Systems, Inc.—On May 31, 2005, we completed the acquisition of 100 percent of the outstanding shares of Gray Hawk Systems, Inc. (“Gray Hawk”). Gray Hawk provides a broad range of intelligence-related services to the homeland security, law enforcement, Intelligence Community and the Department of Defense markets. The acquisition was consummated pursuant to an Agreement and Plan of Merger, dated May 3, 2005, which provided for the merger of a wholly owned subsidiary of ManTech with and into Gray Hawk, with Gray Hawk surviving the merger and becoming a wholly owned subsidiary of ManTech (“ManTech Gray Hawk”).

We believe the Gray Hawk acquisition further solidifies our position as a supplier of services in the high-end intelligence market. It expands our presence in homeland security related missions and compliments our high-end offerings for the Intelligence Community and Department of Defense. Gray Hawk’s capabilities round-out our skills in the end-to-end, intelligence information processing cycle, and give us access to new markets in national defense agencies which we believe will become increasingly important as the Intelligence Reform Act of 2004 continues to unfold.

The purchase price for the Merger was $101.8 million in cash, which included transaction costs of $0.3 million. The purchase price included the full payment of Gray Hawk’s outstanding debt, repurchase of employee stock options by Gray Hawk, transaction costs and other related transaction expenses. Pursuant to the Merger

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Agreement, and as security for the Gray Hawk shareholders’ indemnification obligations, an escrow account in an amount equal to 10% of the adjusted purchase price has been established for a period of one year following the closing of the Merger, which is to be used to satisfy certain indemnification obligations of the shareholders of Gray Hawk.

2004 Acquisition

Acquisition of Certain Assets from Affiliated Computer Services, Inc.—In furtherance of our strategic initiative to expand and enhance our support of the U.S. Air Force, on February 27, 2004, we acquired certain assets from Affiliated Computer Services, Inc. (ACS), a provider of systems engineering, network administration, program management, and communications systems support to Department of Defense customers. The assets acquired from ACS included contracts providing support to the U.S. Air Force Electronic Systems Center’s Information Technology Services Program. Services provided through these contracts include information technology services such as program management, systems engineering, network engineering and administration, test and evaluation, and data management. The purchase price of this acquisition was $6.5 million. On June 1, 2004, we acquired additional assets from ACS for $1.5 million. The assets acquired from ACS include contracts for providing support to NATO.

2003 Acquisitions

Integrated Data Systems Corporation—On February 28, 2003, we acquired 100 percent of the outstanding common shares of Integrated Data Systems (IDS) for a cash purchase price of $62.7 million, net of cash on hand of $2.8 million. The cash purchase price excluded $1.0 million of acquisition-related costs and was subject to an earnout provision. Founded in 1990, IDS delivers technology solutions and products in four core areas: software development, systems engineering/networking, information assurance, and government acquisition/procurement support software. IDS has developed secure, advanced messaging and collaboration applications and solutions in support of a wide variety of national security networks and systems. IDS is also one of Microsoft’s leading certified partners supporting U.S. government classified Intelligence Community programs. Many of the IDS employees have military or intelligence experience and high-level clearances.

MSM Security Services, Inc.—On March 5, 2003, we acquired 100 percent of the outstanding common shares of MSM Security Services, Inc. (MSM), a Maryland-based provider of Personnel Security Investigation (PSI) services to the U.S. government. The cash purchase price was approximately $4.9 million, of which $2.2 million in cash was paid to MSM shareholders and $2.7 million was used to repay existing MSM debt. The cash purchase price excludes $0.2 million of acquisition-related costs and is subject to an earnout provision. MSM specializes in PSI services for the U.S. government, having completed over 250,000 background investigations since its founding in 1978. MSM has active investigation contracts to support the U.S. Customs Service, the Office of Personnel Management, the Department of State, the Intelligence Community, and other federal government agencies.

In February 2005, we reached a final corporate determination to exit the personnel security investigation (PSI) services business and discontinue operations at our MSM subsidiary. We reached the determination to sell our MSM subsidiary after we concluded that the MSM business no longer furthered our long-term strategic objectives. Currently, we intend to sell MSM as a going-concern and are in discussions with potential buyers. We expect to complete the sale or other disposition of the MSM operations by the end of the second quarter 2006. At December 31, 2005, we recorded a loss accrual of $3.6 million on the valuation of these assets based on offers received from potential buyers in early 2006. The loss accrual reflects the write-off of intangible assets including goodwill, net of taxes and a valuation allowance of $1.3 million for deferred state income tax assets. For further information, see Note 16 to the Consolidated Financial Statements in Item 8.

Company Information Available on the Internet

Our internet address is www.mantech.com. We make available free of charge on our internet site our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and any amendments to

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those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act, as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC.

ITEM 1A. Risk Factors

We depend on contracts with the U.S. federal government for substantially all of our revenues. If our relationships with the federal government are harmed, our business could be adversely affected.

We expect that federal government contracts will continue to be the primary source of our revenues for the foreseeable future. We derived approximately 98% of our revenues from our federal government customers, (consisting primarily of customers in the Intelligence Community, the Departments of Defense, State, Homeland Security and Justice, and other U.S. federal government agencies) in each of the last two years. Our business, prospects, financial condition or operating results could be materially harmed if

Among the key factors in maintaining our relationships with federal government agencies are our performance on individual contracts and task orders, the strength of our professional reputation and the relationships of our senior management with our customers.

Federal government spending priorities may change in a manner that harms our business.

Our business depends upon continued federal government expenditures on intelligence, defense and other programs that we support. These expenditures have not remained constant over time. For example, the overall U.S. defense budget declined for periods of time in the late 1980s and the early 1990s. While spending authorizations for intelligence and defense-related programs by the government have increased in recent years, and in particular after the September 11, 2001 terrorist attacks, future levels of expenditures and authorizations for these programs may decrease, remain constant or shift to programs in areas where we do not currently provide services. Our business, prospects, financial condition or operating results could be materially harmed by the following

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Federal government contracts contain provisions that are unfavorable to us.

Federal government contracts contain provisions, and are subject to laws and regulations, that give the government rights and remedies not typically found in commercial contracts. These provisions may allow the government to

If the government terminates a contract for convenience, we may recover only our incurred or committed costs, settlement expenses and profit on work completed prior to the termination. If the government terminates a contract for default, we may not recover even those amounts, and instead may be liable for excess costs incurred by the government in procuring undelivered items and services from another source. We may experience performance issues on some of our contracts. We may receive show cause or cure notices under contracts that, if not addressed to the government’s satisfaction, could give the government the right to terminate those contracts for default or to cease procuring our services under those contracts in the future.

We may be exposed to liabilities or losses from operations that we have or will discontinue or otherwise sell, including our MSM subsidiary.

In February 2005, we reached a final corporate determination to exit the personnel security investigation (PSI) services business and discontinue operations at our MSM subsidiary. Currently, we intend to sell MSM as a going-concern. We have engaged in discussions with potential buyers, and we expect to complete the sale or other disposition of the MSM operations by the end of the second quarter of 2006. However, we cannot assure you that we will complete a transaction under the terms currently being discussed with such parties, or at all. Similarly, we may incur unanticipated additional costs in connection with the sale or disposition of MSM. If we are not able to sell or dispose of MSM on the terms currently contemplated, our business, prospects, financial condition or operating results could be harmed.

In recent years, we have sold or wound down the operations of other businesses as well.

For more information on these discontinued operations, please see Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations—Discontinued Operations and Note 16 to our consolidated financial statements. Our consolidated financial statements reflect, under the heading “Discontinued Operations,” our estimate of the net losses we expected from these operations through the date we estimated they would be disposed, and all losses expected to be realized upon the disposal of these operations. Even after the disposition of these businesses, we may continue to be exposed to some liabilities arising from their prior operations. Additionally, when we sell one of our subsidiaries, the operative contractual agreement may contain provisions that require us to indemnify the purchaser for certain liabilities that arose prior to the sale date but that are discovered afterwards. Even though these liabilities are often capped, until the indemnification period expires, we may continue to be exposed to such liabilities.

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If we fail to comply with complex procurement laws and regulations, we could be liable for various penalties or sanctions.

We must comply with laws and regulations relating to the formation, administration and performance of federal government contracts. These laws and regulations affect how we conduct business with our federal government contracts. In complying with these laws and regulations, we may incur additional costs, and non-compliance may also allow for the assignment of additional fines and penalties, including contractual damages. Among the more significant laws and regulations affecting our business are the following:

Along with agency regulations supplemental to the Federal Acquisition Regulations, comprehensively regulate the formation, administration and performance of federal government contracts

Requires certification and disclosure of all cost and pricing data in connection with contract negotiations

Imposes accounting requirements that govern our right to reimbursement under certain cost-based federal government contracts

Our contracting agency customers periodically review our performance under and compliance with the terms of our federal government contracts. We also routinely perform internal reviews. As a result of these reviews, we may learn that we are not in compliance with all of the terms of our contracts. If a government review or investigation uncovers improper or illegal activities, we may be subject to civil or criminal penalties or administrative sanctions, including

If we fail to comply with these laws and regulations, we may also suffer harm to our reputation, which could impair our ability to win awards of contracts in the future or receive renewals of existing contracts. If we are subject to civil and criminal penalties and administrative sanctions or suffer harm to our reputation, our current business, future prospects, financial condition, or operating results could be materially harmed. In addition, we are subject to industrial security regulations of the Department of Defense and other federal agencies that are designed to safeguard against unauthorized release or access to classified information by foreign nationals. The government may also reform our procurement practices or adopt new contracting rules and regulations, including cost accounting standards, that could be costly to satisfy or that could impair our ability to obtain new contracts.

Unfavorable federal government audit results could subject us to penalties or sanctions, and could harm our reputation and relationships with our customers and impair our ability to win new contracts.

The Defense Contract Audit Agency (DCAA) and other government agencies routinely audit and investigate government contracts. These agencies review a contractor’s performance on its contract, cost structure and

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compliance with applicable laws, regulations and standards. The DCAA also reviews the adequacy of, and a contractor’s compliance with, its internal control systems and policies, including the contractor’s purchasing, property, estimating, compensation and management information systems. Any costs found to be improperly allocated to a specific contract will not be reimbursed, while such costs already reimbursed must be refunded. Therefore, a DCAA audit could materially affect our competitive position and result in a substantial adjustment to our revenues. If a government audit uncovers improper or illegal activities, we may be subject to civil and criminal penalties and administrative sanctions, including termination of contracts, forfeiture of profits, suspension of payments, fines and suspension or debarment from doing business with federal government agencies. In addition, we could suffer serious harm to our reputation if allegations of impropriety were made against us.

We derive significant revenues from contracts awarded through a competitive bidding process.

We expect that a significant portion of our future business will be awarded through competitive bidding. Competitive bidding presents a number of risks, including

We may not be provided the opportunity in the near term to bid on contracts that are held by other companies and are scheduled to expire if the government extends the existing contract. If we are unable to win particular contracts that are awarded through the competitive bidding process, we may be unable to operate in the market for services that are provided under those contracts for a number of years. If we are unable to consistently win new contract awards over any extended period, our business and prospects will be adversely affected.

The government may terminate our federal government contracts at any time.

We derive substantially all of our revenue from federal government contracts that may span one or more base years and one or more option years. The option periods typically cover more than one-half of the contract’s duration. Federal government agencies generally have the right not to exercise these option periods. Additionally, federal government contracts typically contain provisions permitting a government client to terminate the contracts for its convenience. A decision not to exercise option periods or a decision to terminate contracts could result in a substantial adjustment to our revenues and reduce the profitability of these contracts to us.

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We may not accurately estimate the expenses, time and resources necessary to satisfy our contractual obligations.

We enter into three types of federal government contracts for our services: cost-plus, time-and-materials and fixed-price. For our last two fiscal years, we derived revenue from such contracts as follows:

Under cost-plus contracts, we are reimbursed for allowable costs and paid a fee, which may be fixed or performance-based. To the extent that the actual costs incurred in performing a cost-plus contract are within the contract ceiling and allowable under the terms of the contract and applicable regulations, we are entitled to reimbursement of our costs, plus a profit. However, if our costs exceed the ceiling or are not allowable under the terms of the contract or applicable regulations, we may not be able to recover those costs. Under time-and-materials contracts, we are reimbursed for labor at negotiated hourly billing rates and