The United States and its allies are at risk of missile attack from a growing number of states and nonstate terrorist organizations. This growing threat is particularly clear in East Asia, where diplomacy has failed to stop North Korea from developing nuclear weapons and the missiles to deliver them on target, and where China continues the most active nuclear force modernization program in the world. To counter these growing threats, the U.S. should work with its allies, including South Korea and Japan, to develop and deploy missile defenses, including ground-based, sea-based, and air-based components.