Much like Puerto Rico, the American Virgin Islands – more commonly known as the U.S. Virgin Islands – are a U.S. territory. That means that citizens of the Virgin Islands are also citizens of the United States, and a flight to the Virgin Islands is considered a domestic trip for residents of the United States. Although U.S. citizens aren't technically required to show a passport to make this sort of trip, it's often a good idea to have your passport along anyway.
Visiting Other Caribbean Nations
Although you don't technically need a passport to go to or from domestic destinations like the U.S. Virgin Islands, you do need a passport if you decide to make a quick hop to any nearby Caribbean nations, including the Dominican Republic, Haiti, Jamaica or Dominica, or if your itinerary touches on any of these ports. So if you have a passport, it's often easiest and safest to bring it just in case, even if your travel plans don't already include these destinations, or any of the other nearby Caribbean islands.
Proving Citizenship Just In Case
Although U.S. Customs and Border Protection doesn't strictly mandate that you must have your passport to travel to a territory like the U.S. Virgin Islands, it does recommend that you take a government-issued photo ID and a copy of a birth certificate, just in case. Together, these documents prove your identity and your U.S. citizenship. Your passport serves both functions in just one document, and also serves as government-issued photo ID to get you on and off the plane on your way there.
Traveling With a Green Card
If you're a lawful permanent resident of the United States – or in colloquial terms, if you hold a green card – and your itinerary doesn't touch on a foreign port, you don't have to show your green card to come or go from the U.S. Virgin Islands. However, U.S. Customs and Border Protection recommends carrying proof of your lawful permanent resident status on you at all times.
Green card holders don't qualify for a U.S. passport, so if you do travel to Caribbean countries that require a passport, you'll need to use a passport from your country of origin.
Using Enhanced Driver's Licenses
Enhanced driver's licenses can be used to prove both identity and citizenship – that is, the same function as a passport – when traveling by land or sea. But they're not valid for international air travel. So, if you're going only to the U.S. Virgin Islands, you can use your EDL as your government-issued photo ID to get on the plane. But if you're flying to any nearby foreign nations, an EDL won't cut it; you'll need a passport.