Do you need a passport for a cruise?

For closed-loop cruises, those that begin and end at the same US port and stay within the Western Hemisphere, US citizens can often sail with a government-issued photo ID plus a certified birth certificate rather than a passport. That is the rule people rely on, and it is legitimate. Cruises that begin and end in different ports, or that visit destinations outside those rules, require a passport, and individual countries can impose their own entry requirements regardless of the cruise line's minimum.

The reason to carry a passport anyway is the scenario nobody plans for. If you miss the ship at a foreign port, get sick or injured and need to be flown home, or face an emergency at home, you have to enter a foreign country and board an international flight, and only a passport makes that possible without an expensive, slow trip to a US embassy. That single failure mode is why the State Department and most experienced cruisers recommend traveling with one even when it is not strictly required. Check expiration too, many countries require at least six months of validity beyond your travel dates, and some require blank pages. Renew early, since processing times fluctuate and expedited service costs more.