Yes, a valid passport is mandatory for almost all travelers visiting the island of Saint Martin, which is unique for being divided into a French side (Saint-Martin) and a Dutch side (Sint Maarten). Even though there is no "hard border" between the two sides, the island is an international destination. For U.S., Canadian, and European citizens, your passport must be valid for at least six months beyond your date of departure. It is a common misconception that U.S. citizens can use just a birth certificate; while some "closed-loop" cruises departing from and returning to the same U.S. port might allow this under the Western Hemisphere Travel Initiative (WHTI), it is extremely high-risk, as you would be unable to fly home in an emergency without a passport. Furthermore, if you arrive at Princess Juliana International Airport (SXM) on the Dutch side, you must complete an Electronic Entry-Exit Program (ED-Card) before arrival. Always carry your passport when moving between the French and Dutch sides to ensure compliance with local high-fidelity security spot checks.