ABSTRACT The District of Columbia is in the midst of a significant HIV/AIDS epidemic; approximately 3% of District of Columbia residents over the age of 12 years are living with HIV/AIDS. Injection drug use (IDU) accounts for 18% of the living cases of HIV/AIDS in the District. The scientific community has focused increased attention on the need for HIV prevention interventions that can better address the social and structural drivers of HIV risk than would be possible with individual-level interventions. Syringe exchange programs are a perfect example of a proven- effective, structural intervention that could have a tremendous impact on reducing HIV risk for injection drug users. For approximately a decade, Federal policy prohibited the District of Columbia from using its own municipal revenue to support syringe exchange programs; this policy changed with the passage by Congress of HR 2764, The Consolidated Appropriations Act, 2008. The passage of this bill and the subsequent passage of HR 3288, The Consolidated Appropriations Act, 2010 (which removed the Federal ban on funding for syringe exchange) were landmark legislative actions in the history of HIV prevention efforts in the United States. They also represent rare instances in which natural policy interventions have occurred. What remains unknown is whether or not these events are having (or will have) a measurable and significant impact on the growing HIV epidemic in the District of Columbia. The purpose of the proposed project is to: (1) conduct an impact evaluation to determine whether or not the change in syringe exchange funding policy in Washington, DC, is associated with increased access to syringe exchange services, and increased linkage to other relevant HIV prevention services for IDU (i.e., HIV testing, HIV treatment, and addiction treatment); (2) examine whether or not these changes in policy have an impact on the numbers of new cases of HIV infection associated with IDU reported in the District of Columbia; and (3) conduct a policy analysis comparing the Washington, DC, syringe exchange policy experience with those of two other cities (Baltimore, MD, and Philadelphia, PA) that required changes in local policy before funding could be used to support syringe exchange activities in order to determine how these changes in policy affected HIV prevention efforts targeting injection drug using populations. Data from this project will provide evidence of the public health benefit to Washington, DC, that has resulted from these policy changes as well as evidence to demonstrate that changing policies to support syringe exchange services can have substantial impact on the HIV epidemic.