The set of laws which govern passport usage for the United States is the Western Hemisphere Travel Initiative. This set of laws is a direct result of the Intelligence Reform and Terrorism Prevention Act of 2004. The laws are supposed strengthen the border security of the United States while making it easier for U.S Citizens and legitimate foreign visitors to enter the country. The requirements for cruise ships falls under the guidelines for Land and Sea Travel
As of June 1, 2009, the final WHTI regulations went into effect. These regulations state that all Adult Passengers (16 and older) must have a valid passport, passport card, enhanced driver's license, or Trusted Traveler Program card to travel to and from the U.S. Any citizen who doesn't have any documents which will verify citizenship has to present both a proof of citizenship and identification (a birth certificate and driver's license). Any adult going on a cruise must have these documents for re-entry to the U.S.
Any child under the age of 16 does not need a passport. He is allowed to show the original (or a copy) of his birth certificate to regain entry to the U.S. Children who are 16-18 years of age who are cruising with a school or religious group, or sports team with adult supervision may enter the U.S. with the original or a copy of their birth certificates or other proof of citizenship.
If there are non-U.S. citizens on a cruise, they will still need their passport from the country of origin. However, they may be asked to surrender their passport upon embarkation for an immigration inspection; it will be returned to the traveler at the end of their cruise. Some non-U.S. citizens may be eligible to apply for the Visa Waiver Program (a program which allows citizens from some countries to enter the U.S. for up to 90 days without a visa); however, they still need to have a valid passport.
The Department of Homeland Security has made an exception for "Closed-Loop" Cruises. A Closed-Loop cruise is one which originates from an American port, travels only in the western hemisphere, and returns to the same U.S. port (A Caribbean Cruise which leaves from and returns to Miami is a good example). Any travelers on this type of cruise do not need a passport, but will need a copy of their birth certificate and U.S. government-issued ID (i.e. a driver's license) Travelers taking advantage of this must also return on the same ship. Anyone on this type of cruise should note that any foreign country may require a passport for entry.
