States and localities issue debt to finance projects undertaken by government and, in some cases, by the private sector (bonds issued by states and localities to finance either government operations or certain private-sector activities are known as municipal bonds). The federal government subsidizes the issuance of municipal bonds by offering tax preferences that lower the cost of debt incurred for those projects. Government accounts for the bulk of investment in infrastructure today, largely reflecting the likelihood that infrastructure would otherwise be under-supplied. Recently, however, the private sector has been viewed as an increasingly viable source of financing; from that perspective, a key issue is whether the government should offer incentives (say, through tax subsidies or other favorable regulation) to encourage such investment. This study, prepared jointly by the Congressional Budget Office and the Joint Committee on Taxation, focuses on the use of tax-preferred debt to finance infrastructure. After an overview of investment in infrastructure in the United States--who pays for it, how much it costs, and the federal government's role in financing it--the study: (1) Discusses some of the advantages and disadvantages of tax preferences as a means of providing federal financial support for investment in infrastructure; (2) Outlines the rules applicable to the issuance of tax-exempt and tax-credit bonds; (3) Reviews historical trends in the issuance of tax-preferred bonds and quantifies the reliance of state and local governments and the private sector on such bonds as a means of financing their capital spending; and (4) Considers potential efficiency improvements to current tax policy through appropriately structured tax-credit bonds. (Contains 3 tables, 6 figures, 4 boxes and 61 footnotes.)