Nuclear deterrence continues to be an important concept in international relations, despite the dramatic changes since the Cold War. As efforts are made to reduce the number of nuclear weapons to very low levels, with the ultimate goal of elimination, it is important to consider issues such as who is entitled to have nuclear deterrence, how nuclear deterrence operates at very low levels, the proper role of ABM defenses and how to strengthen nonproliferation norms by assuring the security of states without nuclear weapons. One path to resolving these difficult issues may be a greater reliance upon collective defenses by groups of states, using conventional arms.