All valid driving licences issued by a European Union Member State are accepted for rental, and must always be accompanied by a valid identity document. The holder of a driving licence who has been resident in Italy for more than one year is not obliged to convert the licence, but must have it recognised within 90 days by the Driver and Vehicle Licensing Agency.
If you have a driving licence issued by a non-EU foreign State, you need an International Driving Permit or a sworn translation of the licence in order to drive in Italy. Vehicles for which the licence is valid may be driven in Italy, provided that the driver has not resided in Italy for more than one year.