Why GAO Did This Study. By law, GAO annually assesses the Missile Defense Agency's (MDA) progress in developing and fielding a Ballistic Missile Defense System (BMDS). Funded at $8 billion to nearly $10 billion per year, it is the largest research and development program in the Department of Defense (DOD). The program has been managed in 2-year increments, known as blocks. Block 2006, the second BMDS block, was completed in December 2007. GAO assessed MDA's progress in (1) meeting Block 2006 goals for fielding assets, completing work within estimated cost, conducting tests, and demonstrating the performance of the overall system in the field, and (2) making managerial improvements to transparency, accountability, and oversight. In conducting the assessment, GAO reviewed the assets fielded; contractor cost, schedule, and performance; and tests completed during 2007. GAO also reviewed pertinent sections of the U.S. Code, acquisition policy, and the charter of a new missile defense board.