The safety and economic security of the United States depends on the secure use of the world’s seaports and waterways. Homeland Security Presidential Directive-13 (HSPD-13, also referred to as National Security Presidential Directive-41) directs the coordination of U.S. maritime security policy through the creation of a National Strategy for Maritime Security and supporting implementation plans. GAO was asked to evaluate this strategy and its eight supporting plans. This report discusses: (1) the extent to which the strategy and its supporting plans contain desirable characteristics of an effective national strategy, and (2) the reported status of the implementation of these plans. To conduct this work, GAO evaluated the National Strategy for Maritime Security and its supporting plans against the desirable characteristics of an effective national strategy that GAO identified in February 2004, reviewed HSPD-13 and supporting plans, and reviewed documents on the status of the plans’ implementation. Of the six desirable characteristics of an effective national strategy that GAO identified in 2004, the National Strategy for Maritime Security and its eight supporting implementation plans address four and partially address the remaining two. Documents provided by the Maritime Security Working Group–an interagency body responsible for monitoring and assessing the implementation of the maritime strategy–indicate that the implementation status of the eight supporting plans varies. For example, as of November 2007, implementation of one plan had been completed, while another has reached the assessment phase (e.g., lessons learned and best practices), and a third has reached the execution phase (e.g., exercises and operations). The other five plans remain primarily in the planning phase. The working group is monitoring the implementation of 76 actions across the plans, and reported 6 of these are completed and 70 are ongoing.