According to the "frequent traveler" consensus on Reddit and official CBP rules in 2026, the answer depends on your cruise type. If you are a U.S. citizen on a "Closed-Loop" cruise (starting and ending at the same U.S. port, like Miami to Nassau and back to Miami), you do not strictly need a passport; you can use a government-issued photo ID and an original birth certificate. However, the "Reddit wisdom" almost universally recommends bringing a passport anyway. The primary reason is that if you have a medical emergency in the Bahamas or miss the ship and need to fly home, you cannot board an international flight to the U.S. without a valid passport. A birth certificate only works for sea travel. For non-U.S. citizens or for "Open-Loop" cruises (starting in Miami but ending in San Juan, for example), a passport is 100% mandatory. In short: while you can legally get by with a birth certificate on most standard Bahamas cruises, the risk of being "stuck" abroad without a passport makes it a highly discouraged practice among seasoned cruisers in 2026.