If you are a U.S. citizen and do not have your birth certificate for a "Closed-Loop" cruise (one that starts and ends at the same U.S. port), you cannot board the ship unless you have a valid U.S. Passport. For these specific cruises, a state-certified birth certificate paired with a government-issued photo ID (like a driver's license) is the minimum legal requirement. If you lack both a passport and a certified birth certificate, you will be denied boarding at the pier with no refund. It is important to note that hospital "souvenir" certificates with baby footprints or uncertified photocopies are not accepted; it must be an original or a certified copy from the Vital Statistics office. In 2026, Carnival and other lines "strongly recommend" a passport for everyone. This is because if you have a medical emergency or miss the ship in a foreign port, you cannot fly back to the U.S. without a passport, even if you were allowed to sail without one. If you find yourself without these documents, you must apply for an expedited passport immediately.