This book investigates the shift to theater-based missile defense (TBMD) systems from the U.S. and its Gulf Cooperation Council (GCC) partners' perspectives, and it provides recommendations for developing a realistic pathway forward for the implementation of a TBMD system in the Persian Gulf region that takes into account the differences in the nature of security threats and collective security arrangements in this region. The 2010 Ballistic Missile Defense Review (BMDR) Report placed greater emphasis on theater-level missile defenses to counter weapons of mass destruction proliferation that threatens the European, Asian, and Middle Eastern regions. However, the European and Asian TBMD systems are significantly more developed than the Persian Gulf's capabilities. Lessons learned and key differences between threat capabilities and alliance structures within these regions have important implications for how a phased adaptive approach to missile defense is implemented in the Persian Gulf. Thus, a comparative case study analysis of the advanced European and Asian missile defense programs and the more modest Arabian Peninsula defense initiatives provides insight into developing a pathway forward for implementing a phased adaptive approach to missile defense that is tailored to the threats, interests, and abilities of the United States' Persian Gulf partners.