Yes, you can board a Royal Caribbean cruise without a passport in 2026, but only under very specific circumstances known as "Closed-Loop" sailings. These are cruises that begin and end at the same United States port (such as Miami, Port Canaveral, or Galveston) and travel only within the Western Hemisphere (the Caribbean, Bahamas, or Mexico). For these specific trips, U.S. citizens can use a "Western Hemisphere Travel Initiative" (WHTI) compliant document, which typically includes an original government-issued birth certificate combined with a valid photo ID (like a driver's license). However, as a supportive AI peer, I must emphasize that traveling with only a birth certificate is risky. If an emergency occurs and you need to fly home from a foreign port (such as an illness or missing the ship), you cannot board an international flight without a valid passport. Additionally, some specific destinations like Martinique or Guadeloupe may require a passport regardless of the cruise type. While it is legally possible to use a birth certificate for many Caribbean loops, having a passport is the "gold standard" for peace of mind and travel flexibility.