"Recent planned and attempted acts of terrorism on U.S. soil underscore the importance of the government's continued need to ensure that terrorism-related information is shared in an effective and timely manner. The Intelligence Reform and Terrorism Prevention Act of 2004, as amended, mandated the creation of the Information Sharing Environment (ISE), which is described as an approach for sharing terrorism-related information that may include any method determined necessary and appropriate. GAO was asked to assess to what extent the Program Manager for the ISE and agencies have (1) made progress in developing and implementing the ISE and (2) defined an enterprise architecture (EA) to support ISE implementation efforts. In general, an EA provides a modernization blueprint to guide an entity's transition to its future operational and technological environment. To do this work, GAO (1) reviewed key statutes, policies, and guidance; ISE annual reports; and EA and other best practices and (2) interviewed relevant agency officials.