Requirements for Entering Foreign Countries
Review the US State Department's country list to learn the requirements for US citizens entering specific foreign countries. This site includes conditions in your region of travel that may affect your safety and security and specific entry requirements such as passports, visas, immunizations, medical information, and additional fees.
All persons, including U.S. citizens, traveling by air between the United States and Canada, Mexico, Central and South America, the Caribbean, and Bermuda will be required to present a valid passport, Air NEXUS card, or U.S. Coast Guard Merchant Mariner Document, or an Alien Registration Card, Form I-551 (if applicable).
The passport requirement does NOT apply to U.S. citizens traveling to or returning directly from a U.S. territory. U.S. citizens returning directly from a U.S. territory are not considered to have left the United States and do not need to present a passport. U.S. territories include the following: Guam, Puerto Rico, the U.S. Virgin Islands, American Samoa, Swains Island, and the Commonwealth of the Northern Mariana Islands.
Additional Resources from the US Department of State