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.