Since 2010, the United States has suffered grave damage to national security and an increased risk to the lives of U.S. personnel due to unauthorised disclosures of classified information by individuals with authorised access to defense information systems. Congress and the President have issued requirements for structural reforms and a new program to address insider threats. A 2014 House Committee on Armed Services report included a provision that the United States Government Accountability Office (GAO) assess The Department of Defense's (DOD) efforts to protect its information and systems. This book evaluates the extent to which DOD has implemented an insider-threat program that incorporates minimum standards and key elements; DOD and others have assessed DOD's insider-threat program; and DOD has identified any technical and policy changes needed to protect against future insider threats. Furthermore, the book evaluates the extent to which DOD has reflected insider threat considerations in its force protection policies and other guidance; shared actions that U.S. installations have taken to protect against insider threats; and implemented recommendations from the official reviews of the 2009 Fort Hood and 2013 Washington Navy Yard shootings.