The Common Access Card, also commonly referred to as the CAC is a smart card about the size of a credit card.[1] It is the standard identification for Active Duty United States Defense personnel, to include the Selected Reserve and National Guard, United States Department of Defense (DoD) civilian employees, United States Coast Guard (USCG) civilian employees and eligible DoD and USCG contractor personnel.[1] It is also the principal card used to enable physical access to buildings and controlled spaces, and it provides access to defense computer networks and systems.