Whether you can disembark at a port without a passport depends on the nature of your cruise and the local laws of the destination. On "Closed-Loop" cruises (starting and ending at the same U.S. port) visiting regions like the Caribbean, Mexico, or Bermuda, U.S. citizens can often use a birth certificate and government-issued photo ID instead of a passport. However, many foreign ports and cruise lines "strongly recommend" a passport for all guests. If you don't have one and the ship is forced to dock at an alternate port due to weather or an emergency, you might be barred from going ashore. Furthermore, if you miss the ship or have a medical emergency, you cannot fly back to the U.S. from a foreign country without a valid passport book, making it a significant travel risk.