Entry requirements for St. Maarten (Sint Maarten), the Dutch side of the island, strictly require a valid U.S. passport for all air travelers. While some "closed-loop" cruises (those that start and end at the same U.S. port) may technically allow U.S. citizens to travel to certain Caribbean ports with only a birth certificate and a government-issued photo ID, St. Maarten’s local immigration laws frequently mandate a passport for all international arrivals. Furthermore, travelers must complete an Electronic Health Authorization System (ED-Card) online before landing. If you are a U.S. permanent resident (Green Card holder), you must still present your valid national passport and your residency card. For those arriving by private boat or air, carrying a passport is the only guaranteed way to avoid being denied entry or facing significant legal delays at the border, as the island's dual French/Dutch governance means security protocols are aligned with European standards.