Do I need an International Driving Permit to drive in the US? I have read that it depends on state to state. Suppose, for instance, that I need to rent a car in California. I have a valid Italian (or European) driving licence. Do I need to have an IDP to drive in California?
No, the International Driving Permit is not required for California.
See the information on the California Department of Motor Vehicles site: https://www.dmv.ca.gov/portal/dmv/detail/dl/dl_info#international
The State of California does not recognize an International Driving Permit (IDP) as a valid driver license. California does recognize a valid driver license that is issued by a foreign jurisdiction (country, state, territory) of which the license holder is a resident.
The IDP is only a translation of information contained on a person's foreign driver license and is not required to operate a motor vehicle in California.
I have seen claims that some car rental companies will require an IDP. I doubt this would ever be an issue, as long as your driver's license is comprehensible to an English speaker, but you might want to check to confirm this.
My Italian office-mate held both a USA and Italian drivers license. When pulled over for speeding, which happened often, offering the Italian license usually made the cop too lazy to research what to do, so no ticket. Never a question about driving legally on the license.