Personnel security clearances allow government and contractor employees to gain access to classified information that, through unauthorized disclosure, can in some cases cause exceptionally grave damage to U.S. national security. Events-such as the May 2010 disclosure of classified documents to Wikileaks, the June 2013 disclosure of classified documents by a former National Security Agency contractor, and the September 2013 shooting at the Washington Navy Yard-illustrate the danger that can be posed from insider threats, which involve individuals with authorized access to government resources and information. While much attention has been paid to the processes for granting a personnel security clearance equally important are the processes governing whether individuals who have personnel security clearances should retain their access to classified information. If an individual's circumstances change in a manner that raises security concerns regarding whether he or she should continue to be entrusted with access to classified information, then processes exist to take away, or revoke, an individual's eligibility to access classified information, and for that individual to appeal that decision.