The Common Access Card (CAC) is a smart card used by the United States Department of Defense. It serves as a primary identification card for military personnel, civilian employees, and eligible contractors. The CAC provides access to secure facilities and systems, ensuring that only authorized individuals can enter sensitive areas or use specific services. In addition to identification, the CAC contains a microchip that stores personal information and digital certificates. These certificates enable secure email communication and access to various government websites. The CAC is an essential tool for maintaining security and efficiency within the U.S. military and related organizations.