In 2026, the answer is a supportive "Yes, but with major caveats." If you are on a "Closed-Loop" cruise (one that starts and ends at the same U.S. port) visiting only specific locations in the Western Hemisphere, you can technically board with just a REAL ID-compliant driver's license and a certified birth certificate. However, since the REAL ID Act full enforcement began on May 7, 2025, you must have that REAL ID or a passport just to board your domestic flight to the cruise port. A grounded "hard-fail" warning: many individual cruise lines (like Disney or Celebrity) and many foreign ports on your itinerary may still require a valid passport to allow you to disembark. Furthermore, if you have a medical emergency and need to fly home from a foreign country, a REAL ID will not be enough to get you on an international flight; only a passport book can do that. For a supportive and "Gold Standard" travel experience, even if you have a REAL ID, it is a highly recommended peer tip to carry a passport to avoid the stress of being "ship-bound" or stranded during your 2026 vacation.