Technically, there is no minimum age to require a passport for international travel; even a newborn baby needs a valid passport if the itinerary demands it. However, for U.S. citizens, the rules depend heavily on the cruise route. On a "closed-loop" cruise—one that begins and ends at the same U.S. port and stays within the Western Hemisphere—passengers of any age (including infants) can often travel with just a certified birth certificate and a government-issued photo ID (for those 16 and older). If the cruise is "open-loop" (ending in a different port than it started) or visits regions outside the Caribbean, Mexico, or Canada, a passport is mandatory for everyone regardless of age. In 2026, travel experts strongly recommend that all cruisers, even infants on closed-loop trips, carry a valid passport. This is because if an emergency occurs—such as a medical evacuation or a missed ship departure—you cannot fly back to the U.S. from a foreign country using only a birth certificate. Therefore, while you might not "need" it legally for some specific routes, it is the only document that guarantees you can return home by air in a crisis.