Visas are not needed by U.S., Canadian, Irish, Australian, New Zealand, or British citizens for visits of less than 3 months. You do need a valid passport unless you're a citizen of another E.U. country (in which case, you need only an identity card, although we always recommend that you carry a passport anyway).
Safeguard your passport in an inconspicuous, inaccessible place like a money belt. If you lose it, visit the nearest consulate of your native country as soon as possible for a replacement.
Passports -- For an up-to-date, country-by-country listing of passport requirements around the world, go to the "Foreign Entry Requirement" Web page of the U.S. State Department at http://travel.state.gov.
