Although it is not necessary to have a passport when you cruise from a US port to a foreign port we recommend that you do purchase one for you own benefit.
If your ship leaves a US port and is returning to a US port you will be able to travel with a Certified Birth Certificate. But in the event that you have an emergency or need to fly back home you will not be able to re-enter the US except via the port & ship that you departed on. The US will not allow you to fly home without a passport.
Passports are reasonably priced considering it is an investment that lasts for 10 years. And if you plan to do extensive traveling/cruising outside the US it is almost a necessity. It is a necessity if you plan to fly anywhere out of or back into the US.
We never know when an emergency will arise while we are on vacation and have a need to get home quickly. Also it's a good idea to purchase travel insurance before you leave in the event you do have an emergency and have to cut your trip short or do not get to take your trip you can be reimbursed for most if not all of your expenses incurred in purchasing your tickets. We will be happy to help you pick the best travel insurance to meet your needs!
We have all heard the horror stories. Dropped your wallet overboard? Lost your documents. Donkey ate my passport...
A good idea before you travel is to make a copy of all your Identification documents: Passports, Driver's License, Birth Certificate, credit cards, etc. Keep these copies in a safe place in the event your items are lost or stolen while traveling you should be able to have the document copies faxed or wired to you by a family member, lawyer, or someone you trust, to a consulate or local fax station. It is also a good idea to have copies of these documents with your luggage or left in a locked safe or case in your room. Always be aware of your surroundings when out and about and take care to secure your belongings wherever you go. Your travel agent can also keep a copy of your passport on file if you are a frequent traveler to save time when booking travel for you. They won't have to ask for your documentation numbers and expiration dates every time. And they will also be able to fax those documents to you in the event of an emergency.