This book explores the National Defense Strategy (NDS) which serves as the Defense Department's capstone document in a long-term effort. It flows from the NSS and informs the National Military Strategy. It also provides a framework for other DoD strategic guidance, specifically on campaign and contingency planning, force development, and intelligence. It reflects the results of the 2006 Quadrennial Defense Review (QDR) and lessons learned from on-going operations in Iraq, Afghanistan, and elsewhere. It addresses how the U.S. Armed Forces will fight and win America's wars and how they seek to work with and through partner nations to shape opportunities in the international environment to enhance security and avert conflict. The challenges that the United States, our allies and our partners face are examined in this book, including violent transnational extremist networks, hostile states armed with weapons of mass destruction, rising regional powers, emerging space and cyber threats, natural and pandemic disasters, and a growing competition for resources. The Department of Defense must respond to these challenges while anticipating and preparing for those of tomorrow.