According to your nationality, the length and the reason of your stay, you should have a visa before leaving. In this case you should make a request for it at the Italian consulate in your own country.
The addresses are available at www.esteri.it/ita/2_11_6.asp
, the website of the Italian Ministry of Foreign Affairs.
For the EU citizens a valid identity card is enough. For those under 15 years an identity certificate valid for travel abroad is required; For those over 15 years an identity card valid for travel abroad is enough. For those who are younger, a written statement on the parent’s identity card is required.
For citizens from other country the passport and in some cases the visa are compulsory.
Are you EU citizens? Before leaving, ask your local health authority for an “European form E.111” . Through you can obtain the refund the health costs once come back.