EXHIBIT 21.1

Subsidiaries of the Company

 1st Tier

— ManTech Command Control Systems Corporation, a Virginia corporation

— ManTech Information Systems &Technology Corporation, a Virginia corporation

— ManTech Security & Mission Assurance Corporation, a Delaware corporation

— ManTech Solutions & Technologies Corporation, a Virginia corporation

— ManTech Systems Engineering Corporation, a Virginia corporation

— ManTech Environmental Corporation, a Virginia corporation

— ManTech Support Technology, Inc., a Virginia corporation

— NSI Technology Services Corporation, a California corporation

— ManTech Advanced Systems International, Inc., a Virginia corporation

— ManTech Telecommunications and Information Systems Corporation, a Delaware corporation

— ManTech Europe Systems Corporation, a Virginia corporation

— ManTech Australia Pty. Ltd., a corporation organized and existing under the laws of the Commonwealth of Australia

— ManTech Australia International, Inc., a Virginia corporation

— ManTech U.K. Systems Corporation, a Virginia corporation

— ManTech Advanced Development Group, Inc., a California corporation

— ManTech Security Technologies Corporation, a Virginia corporation

— ManTech Gray Hawk Systems, Inc., a Virginia corporation

— ManTech GRS Solutions, Inc., a Maryland corporation

 2nd Tier

— Technology Management Corporation, a Virginia corporation

— ManTech Systems Corporation, a New Jersey corporation

— ManTech Systems Solutions Corporation, a Virginia corporation

— MASI U.K. Limited, a corporation organized and existing under the laws of the United Kingdom

— Field Support Services Muhendislik Ltd. Sti., a corporation organized and existing under the laws of Turkey

— Redesmundial, S.A., a corporation organized and existing under the laws of the Republic of Panama

— ManTech Europe, Ltd., a corporation organized and existing under the laws of the United Kingdom

— ManTech Test Systems, Inc., a Virginia corporation

— ManTech Environmental Research Services Corporation, a Virginia corporation

— DB Data Systems, LLC, a Virginia corporation

— Gray Hawk Technology Solutions, LLC, a Virginia corporation

— Hawkeye Systems, LLC, a Virginia corporation

— Symmetron Holding Corporation, a Virginia corporation

 3rd Tier

— ManTech Advanced Recognition Limited, a corporation organized and existing under the laws of the United Kingdom

— ManTech Database Services Europe Limited, a corporation organized and existing under the laws of the United Kingdom

— Symmetron, LLC, a Virginia corporation