The short answer is: it depends on your specific itinerary, but a Real ID alone is often not enough for international travel, even on a cruise. If you are a U.S. citizen on a "Closed-Loop" cruise—one that begins and ends at the same U.S. port (for example, sailing from Miami to the Bahamas and back to Miami)—you are technically permitted to travel with a government-issued photo ID (which can be a Real ID) combined with an original or certified copy of your birth certificate. However, a Real ID is just a more secure version of a standard driver's license; it does not serve as proof of citizenship on its own. If your cruise is not closed-loop (for example, you depart from Fort Lauderdale but end in Barbados), a valid U.S. Passport is mandatory. Even on closed-loop cruises, travel experts and cruise lines strongly recommend a passport over a Real ID/birth certificate combo. If an emergency occurs—such as a medical evacuation or a missed ship—and you need to fly back to the U.S. from a foreign Caribbean port, you cannot board an international flight with just a Real ID; you would be stuck at the U.S. embassy waiting for emergency travel documents. Therefore, while a Real ID might get you onto certain ships, it offers significantly less protection and flexibility than a passport.