Beginning January 23, 2007, the U.S. Department of Homeland Security and the U.S Department of State require that all citizens of the United States, Canada, Mexico, South and Central America, Bermuda, and the Caribbean MUST present a valid passport or other acceptable documents to enter the U.S. when arriving by air from any part of the Western Hemisphere.
The Western Hemisphere Travel Initiative (WHTI) requires that all persons, including U.S. citizens, entering the United States from the Americas, Canada, Mexico, the Carribbean, and Bermuda will be required to have a passport (unless traveling with a U.S. Permanent Resident Card, asylee or refugee document, Merchant Mariner's Document, or NEXUS Air Card) to enter the United States.