Ideological differences between the US and its greatest antagonist, the Soviet Union, have been the underpinnings to the majority of foreign politics since the end of World War II. In the 50 years following, the global community lived under both the blanket and shadow of nuclear arms as the two superpowers kept their arsenals and the concept of nuclear deterrence at the center of their respective national security strategies. The United States foremost objective was singular in scope: to prevent the Soviet Union from attacking the United States and its allies and protect US interests abroad. To this purpose the country designed and built a diverse and survivable nuclear force coupled with an extremely effective conventional capability against a singular adversary. Primarily designed around the US nuclear triad and the North Atlantic Treaty Organization (NATO) alliance, this strategy was relatively successful against Soviet communist expansion. However, as stated as early as 2001 and reiterated in the 2006 Quadrennial Defense Review (QDR), large state actors are no longer the sole primary threat. While they remain of interest, current challenges include newly emerging powers, hostile regimes, and non-state/non-governmental actors who may not respond in-kind to the traditional concepts of deterrence. This book will argue that though the utility of the Cold War-era nuclear deterrent strategy will likely remain effective towards those adversaries who respond to the threat of coercive punishment, policy makers will be challenged to develop more adaptive, flexible and uniquely tailored deterrent strategies to counter future national security threats. While US policy recognizes the need to deter all forms of weapons of mass destruction (WMD), this book focuses primarily on the nuclear element.