A passport book is mandatory for all international air travel.
A passport card may be used for entry into the United States at land borders or seaports from Canada, Mexico, the Caribbean, and Bermuda.
U.S. passport booklets are recognized for travel to most countries and certain purposes. However, you may need a visa for entry into these countries, so it’s essential to consult with your travel advisor for proper guidance before your trip.
By law, a valid, unexpired U.S. passport (or passport card) serves as definitive proof of U.S. citizenship, holding the same legal weight as certificates of naturalization or citizenship, provided they are issued to a U.S. citizen for the full period permitted by law. U.S. law does not restrict citizens from obtaining passports from other countries, but they must use their U.S. passport for entry and exit from the United States.