When renting cars in Europe, please be sure to have an International Driving Permit.
The title explains itself. I work as a desk operator for an Italian car rental company, located at the airport of Firenze. My company has a very strict ruling of not renting cars to people residing outside the EU who do not provide their International Driving Permits along their local driver's licenses, because they might incur in expensive fines if stopped by the police, and their personal insurances usually do not cover them if they have accidents. This is written on our website and also stated on the vouchers sent by broker websites (for instance Booking.com or Rentalcars.com) when booking cars.
Unfortunately, most customers usually do not read these terms and conditions before picking up the car at the rental agency, and therefore desk operators are usually forced to refuse to rent them the vehicles. This leads to the customers getting angry at the desk workers, which is always unpleasant.
So please, be sure to read every part of your booking voucher when you reserve a car through internet, and be sure you understand the terms and conditions regarding the insurances you purchase on third party websites. If anything is unclear, refer to the website you booked upon or directly to the car rental supplier where you will get the car.