 Like a U.S. passport book, the passport card is only issued to U.S. nationals exclusively by the U.S. Department of State, is compliant to the standards for identity documents set by the REAL ID Act and can be used as proof of U.S. citizenship.The passport card allows its holders to travel by domestic air flights within the United States, and to travel by land and sea within part of North America.However, the passport card cannot be used for international air travel.