The Department of Homeland Security (DHS) and the Department of Defense (DOD) both have systems that track varying levels of detail related to revocations of employees' security clearances. DHS's and DOD's data systems could provide data on the number of and reasons for revocations, but they could not provide some data, such as the number of individuals who received a proposal to revoke their eligibility for access to classified information, which means that the total number of employees affected by the revocation process is unknown. Personnel security clearances allow people access to classified information that, through unauthorised disclosure, can cause exceptionally grave damage to U.S. national security. In light of recent events, having a high-quality process to determine whether an individual's eligibility to access classified information should be revoked has become increasingly important. DOD and DHS grant the most clearances in the executive branch, and the Director of National Intelligence is responsible for, among other things, oversight of clearance eligibility determinations. This book evaluates the extent to which the agencies track data on these processes; consistently implement government-wide requirements and exercise oversight over these processes; and determine outcomes for employees whose clearances were revoked.