Book excerpt: In the past five years, Russia, China, and others have accelerated their development of hypersonic missiles to threaten U.S. forces in the homeland and abroad. The current Ballistic Missile Defense System, largely equipped to contend with legacy ballistic missile threats, must be adapted to this challenge. The same characteristics that make hypersonic missiles attractive may also hold the key to defeating them. This CSIS report argues how a new hypersonic defense architecture should exploit hypersonic weapons’ unique vulnerabilities and employ new capabilities, such as a space sensor layer, to secure critical nodes. These changes are not only necessary to mitigate the hypersonic threat but to defeat an emerging generation of maneuvering missiles and aerial threats.