Passport law changes quickly, and while it used to be true that one could visit Mexico, Canada and the Caribbean with only a driver’s license and birth certificate, that’s not always the case these days. We strongly recommend that all travelers have a passport to prevent any problems.
This is the official word regarding ”Closed Loop” cruises in the Western Hemisphere:
U.S. citizens who board a cruise ship at a port within the United States, travel only within the Western Hemisphere, and return to the same U.S. port on the same ship may present a government issued photo identification, along with proof of citizenship (an original or copy of his or her birth certificate, a Consular report of Birth Abroad, or a Certificate of Naturalization). Please be aware that you may still be required to present a passport to enter the foreign countries your cruise ship is visiting. Check with your cruise line to ensure you have the appropriate documents.
If you are traveling to the Eastern hemisphere, such as on our cruise to Greece, you will need to have a passport, and visas will be arranged in concert with the travel agency and cruise line depending on local requirements.