Essential for travel in or out of any country!  You will need a passport to cross any border between two countries. It will also be required

Also a good idea:

• Take a photo copy of your itinerary, passport, credit cards, travel insurance documents, important phone numbers and keep them separate from the originals, in case of lost or theft. A good idea is to scan them in and e-mail copies of them to a yahoo or hotmail account registered in your name and keeping it in your inbox. That way even if you loose everything, you have access to a copy of everything.
• Leave a copy with relatives at home
• Check that your passport will be valid for at least six months beyond the period of you plan to be traveling and that there is enough blank pages for the necessary stamps – one page per country you are visiting is a safe norm to work on.