"As the fourth comprehensive review of our military since the end of the Cold War, the Quadrennial Defense Review (QDR) builds on our experience with the policy and forces of the 1991 Base Force Review, the 1993 Bottom-Up Review (BUR), and the 1995 Commission on Roles and Missions of the Armed Forces (CORM). As a result of those reviews, we made significant adjustments in our forces, procedures, and organizations. We have also accumulated a wealth of experience in a new and constantly changing security environment. That experience tells us that we have the finest military force in our nation's history, with unsurpassed professionalism and capability. Nevertheless, this is a propitious time to reexamine our assumptions, programs, and operations. Indeed, the rapid rate of change in the world since the end of the Cold War underscores the importance of undertaking such a reexamination on a regular basis. The QDR is required by the Military Force Structure Review Act, which was included as part of the National Defense Authorization Act for Fiscal Year 1997. The Department of Defense designed the QDR to be a fundamental and comprehensive examination of America's defense needs from 1997 to 2015: potential threats, strategy, force structure, readiness posture, military modernization programs, defense infrastructure, and other elements of the defense program. The QDR is intended to provide a blueprint for a strategy-based, balanced, and affordable defense program."
Quadrennial Defense Review: http://www.defense.gov/qdr/