The Missile Defense Agency (MDA) has spent more than $80 billion since its initiation in 2002 and plans to spend $44 billion more by 2016 to develop, produce, and field a complex integrated system of land-, sea-, and space-based sensors, interceptors, and battle management, known as the Ballistic Missile Defense System (BMDS). Since 2002, National Defense Authorization Acts have mandated that GAO prepare annual assessments of MDA's ongoing cost, schedule, testing, and performance progress. This report assesses that progress in fiscal year 2011. To do this, GAO examined the accomplishments of the BMDS elements and supporting efforts and reviewed individual element responses to GAO data collection instruments. GAO also reviewed pertinent Department of Defense (DoD) policies and reports, and interviewed a wide range of DoD, MDA, and BMDS officials. GAO makes seven recommendations to the Secretary of Defense to reduce concurrency and strengthen MDA's near- and long-term acquisition prospects. DoD concurred with six recommendations and partially concurred with one related to reporting on the cause of the Aegis BMD Standard Missile-3 Block IB test failure before committing to additional purchases. DoD did not agree to tie additional purchases to reporting the cause of the failure. DoD's stated actions were generally responsive to problems already at hand, but did not consistently address implications for concurrency in the future, as discussed more fully in the report.