Concern over terrorist attacks since 2001 has directed attention to potential vulnerabilities of the nation’s water and wastewater systems. The Environmental Protection Agency (EPA), which leads federal efforts to protect the water sector, initiated a research program in 2002 to address immediate research and technical support needs. This report, conducted at EPA’s request, evaluates research progress and provides a long-term vision for EPA’s research program. The report recommends that EPA develop a strategic research plan, address gaps in expertise among EPA program managers and researchers, and improve its approaches to information dissemination. The report recommends several high-priority research topics for EPA, including conducting empirical research in behavioral science to better understand how to prepare people for water security incidents.