On May 7, 2009, the Government Printing Office (GPO) published a 266-page document on its Web site that provided detailed information on civilian nuclear sites, locations, facilities, and activities in the U.S. At the request of the Speaker of the House, this report determines: (1) which U.S. agencies were responsible for the public release of this information and why the disclosure occurred; and (2) what impact, if any, the release of the information has had on U.S. national security. In performing this work, the report analyzed policies, procedures, and guidance for safeguarding sensitive information and met with officials from four executive branch agencies involved in preparing the document, the White House, the House of Rep., and GPO. Illus.