Passport and Visa for Italy:
EU citizens and those of Iceland, Norway and Switzerland do not need a visa and can enter the country with a valid identity document.
Citizens of Australia, New Zealand, USA, Brazil, Canada, Israel and Japan do not need visas either as long as they remain in the country for less than 90 days. They do need to have their passport in order however.
Citizens from other countries should obtain a visa at the Italian embassy or consulate in their country of origin. There you will be informed about what documents to request and hand in and of the cost of the operation (although you can consult this through the link).