This Congressional Budget Office (CBO) paper describes the trends in public spending for transportation and water infrastructure since 1956. CBO focuses on spending for highways and roads, mass transit, rail, aviation, water transportation, water resources such as the construction and maintenance of dams and levees, and water supply and wastewater treatment. Those types of infrastructure, which draw heavily on federal resources, share the economic characteristics of being relatively capital intensive and producing services under public management that facilitate private economic activity. They are typically the types examined by studies that attempt to calculate the payoff, in terms of benefits to the economy, from government funding of infrastructure. The paper reports public spending both for capital and for operation and maintenance. Capital spending is for the purchase, construction, rehabilitation, and improvement of physical infrastructure. Spending for operation and maintenance is composed of expenditures that are generally required to provide the services needed for infrastructure to function and that are often necessary for the repair and safe operation of existing infrastructure. (In some cases-as with air traffic control services, for instance-the costs can be sizable.)