Since the terrorist attacks of September 11, 2001, the nation?s ports and waterways have been viewed as potential targets of attack. The Department of Homeland Security (DHS) has called for using risk-informed approaches to prioritize its investments, and for developing plans and allocating resources that balance security and the flow of commerce. The U.S. Coast Guard?a DHS component and the lead federal agency responsible for maritime security?has used its Maritime Security Risk Analysis Model (MSRAM) as its primary approach for assessing and managing security risks. GAO was asked to examine (1) the extent to which the Coast Guard?s risk assessment approach aligns with DHS risk assessment criteria, (2) the extent to which the Coast Guard has used MSRAM to inform maritime security risk decisions, and (3) how the Coast Guard has measured the impact of its maritime security programs on risk in U.S. ports and waterways. GAO analyzed MSRAM?s risk assessment methodology and interviewed Coast Guard officials about risk assessment and MSRAM?s use across the agency.