In this presentation, CBO examines the size of Department of Defense (DoD) budgets over the 1980–2019 period. Accounting for differences in the size of the military, DoD’s base budget (which excludes war costs such as those for the conflicts in Afghanistan and Iraq) has increased substantially over that period in inflation-adjusted terms. CBO’s analysis of individual portions of DoD’s budget indicates that the cost increases are broad-based, including increases in personnel costs, operation and maintenance costs, and costs to develop and purchase weapon systems.