The present volume, Reposturing the Force: U.S. Overseas Presence in the Twenty-first Century, is the twenty-sixth in the Newport Papers monograph series, published since 1991 by the Naval War College Press. Its primary aim is to provide a snapshot of a process-the ongoing reconfiguration of America's foreign military "footprint" abroad-that is likely to prove of the most fundamental importance for the long-term security of the United States, yet has so far received little if any systematic attention from national security specialists and still less from the wider public. As such, it serves well the broad mission of the Newport Papers series-to provide rigorous and authoritative analysis, of a sort not readily available in the world of academic or commercial publishing, of issues of strategic salience to the U.S. Navy and the national security community generally. Reposturing the Force is, however, unusual in the manner in which it combines rigor and authoritativeness, for several of its authors are or recently were senior U.S. government officials. Ryan Henry and Lincoln Bloomfield, Jr., have been central figures in the Global Defense Posture Review (initiated by Secretary of Defense Donald Rumsfeld in 2002 as the key mechanism for forcing transformation of the U.S. overseas presence) while serving as, respectively, Principal Deputy Under Secretary of Defense for Policy and Assistant Secretary of State for Political-Military Affairs. As such, they are uniquely positioned to comment on the unfolding of this vast, complex, and extremely sensitive undertaking, many of the details of which are still in flux or are (and likely will remain) classified. For additional perspective on the subject, however, we have felt it important to include also papers by several independent scholars and policy analysts. Robert Harkavy's opening essay helps to place current developments in the American global posture in a larger historical and strategic framework. Andrew Erickson and Justin Mikolay provide an in-depth analysis of the role of Guam in recent thinking and decisions about the posture of the U.S. military in the western Pacific. Finally, Robert Work examines the emerging concept of "sea basing" in Navy and Marine Corps doctrine and force planning, an integral yet so far largely neglected dimension of the American military presence abroad.