As of 2015, most cruises require a passport for travel. In the U.S., an exception is when traveling round-trip to and from the same U.S. port, known as a "closed-loop cruise." However, passports may be required to enter non-U.S. territories during the cruise.
As of 2015, U.S. citizens taking a cruise that originates from and ends in the same U.S. port do not require a passport for re-entry to America. This is true if the cruise goes to U.S. territories, Mexico, Canada, the Caribbean, the Bahamas or Bermuda. However, proof of citizenship, like a birth certificate, and government-issued ID is required for re-entry if one does not have a passport.
Permanent residents require a green card for re-entry, and a passport from their home country is strongly recommended according to Royal Caribbean. Passports may also be required to enter another country that the cruise makes a stop at, especially if the traveler is a non-U.S. citizen. Passports are required for any air travel starting or ending outside the United States.
Cruises originating in one U.S. port and ending in a different U.S. port require passports as of June 2009, according to the U.S. Customs and Border Protection. Passports are also required when departing from a U.S. port and ending up in a non-U.S. port, or vice versa, according to Cruise Travel Outlet.
Some cruise lines require a passport for all cruises, regardless of location traveled. Therefore, it is important for travelers to review passport requirements with their cruise line before traveling.