With the world focused on the nuclear crisis in Iran, it is tempting to think that addressing this case, North Korea, and the problem of nuclear terrorism is all that matters and is what matters most. Perhaps, but if states become more willing to use their nuclear weapons to achieve military advantage, the problem of proliferation will become much more unwieldy. In this case, U.S. security will be hostage not just to North Korea, Iran, or terrorists, but to nuclear proliferation more generally, diplomatic miscalculations, and wars between a much larger number of possible players. This, in a nutshell, is the premise of Underestimated: Our Not So Peaceful Nuclear Future, which explores what we may be up against and how we think about this future. Will nuclear weapons spread in the next 20 years to more nations than just North Korea and possibly Iran? Might they be used and, if so, what might we suffer? Finally, what can be done? Underestimated examines each of these questions. NPEC created the first version of Underestimated in November of 2014. The Strategic Studies Institute published an updated first edition in December of 2015 and a second edition in August of 2018. This second edition includes the very latest citations and research.