Until recently the answer was no. However, effective June 1, 2009 the “closed loop” rule states that a U.S. citizen that departs from a U.S. port and returns to the same port only needs a government issued ID and proof of citizenship (original or certified copy of birth certificate; Naturalization papers; or Consular Report of Birth Abroad issued by Department of State). Any other nationality or itinerary requires a passport. Keep your life simple and carry a passport. You also need to look at any visas you might need and a copy of your medical records is never a bad idea. Ladies, if you use one name for your professional life and another for your married life; especially if your passport is in a different name than your booking, carry a certified copy of your marriage certificate with your passport. Guess how we learned about that one.