Abstract: This research documents the primary strategies used by the US Congress to fund transportation earmarks from the early 1990s to the mid-2000s. It draws on careful analysis of funding bills and primary and secondary sources including government reports, industry and policy newsletters, scholarly articles, and publicly available data on earmarks. It is also informed by interviews with transportation stakeholders involved with earmarks at federal, state, and regional levels. By detailing how Congress pays for earmarks, I show that earmarks do more to redistribute than add to existing transportation resources, and that the intricacy of Congressional funding maneuvers can make earmarks’ fiscal impacts hard to discern. Several implications follow for transportation policy and practice. First, critiques that earmarks increase federal transportation spending are misplaced. While such claims make it easy to discredit national investment in transportation, skepticism is in order when earmarks are invoked to throw out the baby with the bathwater. Second, earmarks’ true costs are related not to increased deficits but rather to opportunity costs incurred when unplanned earmarks replace other investments, particularly projects identified through regional and state planning or competitive selection by an executive agency. Finally, this work suggests productive directions for future earmark reform, such as limiting earmarks to projects in regional or state plans and making explicit for any earmarks in a bill the funding mechanisms that support them. Such steps could lessen the opportunity costs (and administrative inefficiencies) of earmarks, increase transparency in earmarking, and potentially make the practice less objectionable if used to facilitate passage of the long overdue surface transportation authorization bill.