The twenty-fifth Secretary of Defense takes readers behind the scenes to reveal the inner workings of the Pentagon, its vital mission, and what it takes to lead it. The Pentagon is the headquarters of the single largest institution in America: the Department of Defense. The D.O.D. employs millions of Americans. It owns and operates more real estate, and spends more money, than any other entity. It manages the world's largest and most complex information network and performs more R&D than Apple, Google, and Microsoft combined. Most important, the policies it carries out, in war and peace, impact the security and freedom of billions of people around the globe. Yet to most Americans, the dealings of the D.O.D. are a mystery, and the Pentagon nothing more than an opaque five-sided box that they regard with a mixture of awe and suspicion. In this new book, former Secretary of Defense Ash Carter demystifies the Pentagon and sheds light on all that happens inside one of the nation's most iconic, and most closely guarded, buildings. Drawn from Carter's thirty-six years of leadership experience in the D.O.D., this is the essential book for understanding the challenge of defending America in a dangerous world--and imparting a trove of incisive lessons that can guide leaders in any complex organization. In these times of great disruption and danger, the need for Ash Carter's authoritative and pragmatic account is more urgent than ever.