Complexity and uncertainty have characterized the international security environment for the past two decades and will likely continue to do so for the foreseeable future. The rise of new global powers is reshaping the international system. Globalization and rapidly advancing technology continue to empower new, often non-state, actors. The proliferation of weapons of mass destruction is an ongoing concern, and new security challenges—increasing demand for scarce resources, rapid urbanization, climate change, new disease strains and others—are arising.The 2010 Quadrennial Defense Review (QDR) Report describes the security environment and America’s role in the world to provide context for its examination of all the elements of the United States’ national defense plans, programs and policies. The review is conducted in the year after each presidential election, allowing new administrations to write the document that will provide guidance for defense activities for the next four years. The report is submitted to Congress at the time of the President’s February budget request. It outlines the strategy that the Department of Defense is pursuing to meet the challenges and fulfill the role described.