This letter responds to a request that CBO analyze the historical and planned future budgets for the Missile Defense Agency’s Ground-Based Midcourse Defense program. CBO has compiled the amounts of funding that were provided for fiscal years 2008 through 2014 and the Defense Department’s planned budgets for fiscal years 2015 through 2019. All of the budget numbers are based on Department of Defense budget justification documents and are given in nominal dollars (that is, they have not been adjusted for inflation).