GAO determined that since DHS began operations in 2003, it has implemented key homeland security operations and achieved important goals and milestones in many areas, such that it has created and strengthened a foundation for achieving its potential. As it has continued to mature, however, more work remains for DHS in order to address gaps and weaknesses in its current operational and implementation efforts, as well as to strengthen the efficiency and effectiveness of those efforts. DHS's accomplishments include the development of strategies and operational plans, the deployment of workforces, and establishing new or expanding existing offices and programs. GAO assessed specific areas of DHS's operations; namely, border security; aviation security; emergency preparedness and response; chemical, biological, radiological, and nuclear threats; leading and coordinating the homeland security enterprise; implementing and integrating management functions for results; and strategically managing risks and assessing homeland security efforts. Although this report presents no new recommendations, GAO previously made approximately 1,500 recommendations to DHS. DHS has addressed approximately half of them, has efforts in progress to address others, and has taken additional action to strengthen its operations. In commenting on the current report, DHS indicated that it does not address all of DHS's activities. 16 tables and 3 figures