This message is for U.S. citizens.
The question pops up quite often...when will I need a passport? Generally, the answer is "yes" for travel you are undertaking on or after June 1, 2009. However, under the Closed Loop Rule
issued by Customs And Border Protection, some cruise passengers are exempt from the passport requirements and will still be able to cruise on some itineraries with a photo ID and valid birth certificate. The closed loop provision is not always valid. For instance, if you take an Alaskan cruise that starts in Seattle and ends in Anchorage you need a passport. If the cruise starts and ends in Seattle, you don't need a passport. If your cruise starts and ends in Vancouver, you need a passport. Starts in Boston and ends in Montreal? You need a passport. The important thing is it has to begin AND end at the same U.S. port. Given the confusion, it simply makes sense to get a passport and be done with it.
The U.S. State Department passport site
is a useful place to see if you need a passport for other travel.
The staff and management of cruise-chat.com strongly recommends that all Americans get and maintain a passport (in book form, not the passport card).