Summary: Pursuant to a congressional request, GAO reviewed the Department of Energy's (DOE) international nuclear materials tracking system and the proposed cooperation agreement between the United States and the European Atomic Energy Community (EURATOM). GAO noted that: (1) the DOE international nuclear materials tracking system is significantly limited in its ability to track nuclear materials internationally and its replacement system faces a high probability of failure; (2) the Nuclear Regulatory Commission's (NRC) physical security requirements would not apply to EURATOM unless they were reflected in the International Atomic Energy Agency's (IAEA) physical security guidelines; (3) NRC and other reviewing agencies use IAEA physical security guidelines as the criterion for approving the physical protection provided by foreign governments; (4) existing law provides for the transfer of sensitive nuclear technology exclusive of any additional provisions of the U.S.-EURATOM agreement; and (5) specific provisions of U.S.-EURATOM agreement permit the executive branch to grant advance consents for retransfer and reprocessing of certain U.S.-origin nuclear materials.