The Department of Defense (DOD) has increasingly relied on reserve personnel to carry out its military operations. Congress and DOD have taken steps to enhance reserve compensation, such as improving health care benefits. Concerns exist, however, that rising compensation costs may not be sustainable in the future, especially given the nation's large and growing long-range fiscal imbalance. Under the statutory authority of the Comptroller General to conduct work on his own initiative, GAO (1) reviewed how much it has cost the federal government to compensate reserve personnel since fiscal year 2000; (2) assessed the extent to which DOD's mix of cash, noncash, and deferred compensation has helped DOD meet its human capital goals; and (3) evaluated the extent to which DOD's approach to reserve compensation provides transparency over total cost to the federal government. To address these objectives, GAO analyzed budget data and relevant legislation and also interviewed appropriate officials. GAO focused this review on part-time reservists and full-time, active guard and reserve.