For U.S. citizens and permanent residents, a passport is not required to travel between the U.S. mainland and Puerto Rico because it is a U.S. territory. In 2026, you simply need a valid government-issued photo ID that meets REAL ID requirements (which became mandatory at TSA checkpoints on May 7, 2025). This typically means a "star" marked driver's license or a military ID. However, if you are an international traveler, you must treat Puerto Rico like any other part of the United States: you will need a valid passport and, depending on your country of origin, an approved ESTA or a U.S. visa. It is also wise for U.S. citizens to carry a passport if they plan to take a cruise from San Juan that visits non-U.S. islands, or as a backup in case a flight is diverted to a foreign country due to weather or emergencies.