For citizens of the United States, flying to St. Thomas in the U.S. Virgin Islands (USVI) is considered a domestic flight, not an international one. Because the USVI is a United States territory, travel between the mainland and St. Thomas is legally similar to flying between two states. U.S. citizens are not required to present a passport to enter St. Thomas, although it is highly recommended to carry one as it is the easiest form of identification for travel. If you do not have a passport, you must present a government-issued photo ID and an original or certified copy of your birth certificate with a raised seal. However, there is a unique twist: when returning from St. Thomas to the U.S. mainland, you must go through a U.S. Customs and Border Protection pre-clearance process. This is because the USVI is a "separate customs territory" from the mainland. You will be required to fill out a customs declaration form, and your luggage may be inspected to ensure you are not bringing back prohibited agricultural items or exceeding duty-free limits on alcohol and tobacco. So, while the flight itself is domestic, the arrival back home feels a bit like an international entry.