This paper starts by reviewing how defenses fit into larger discussions of strategy, notably discussions of deterrence, defense, extended nuclear deterrence, and extended conventional deterrence. It then discusses some of the dilemmas and debates that have faced American decision makers over the decades regarding ballistic-missile defenses, emphasizing enduring considerations and noting repeated errors. It then turns to the more specific current-day issues for South Korea and other nations in East Asia. Building on the earlier presentation by Dr. Bonomo, it ends by summarizing key policy issues and criteria that might be used by nations of the region in making decisions.