Can you rent a car in Spain with just a US drivers license or do you need an International Driving Permit?
You can rent without an IDP, but if you are caught by the police without one, you may face consequences such as a hefty fine etc.
Ditto Carlos’ response. I’ve never been asked by the rental car agency to show my IDP, but an IDP is required. Better to spend the $20 than to get into an accident and get a large fine for not having one. The rental agency will make a copy of your U.S. license.
To be clear: you need you valid, US drivers license and a valid IDP (both with you and available to show authorities) to be legal to drive in Spain. An IDP is cheap, quick and easy to get.
Just like insurance, you may not feel like you really need it, but if something happens and you don't have them, you will wish you did.
To add to Carlos... driving without an IDP in most of Europe is, legally speaking, as if you were driving without a license. Your US-issued state license by itself is not worth the paper it is written on, again, legally speaking. The IDP sort-of "validates" the license telling whatever officer stops you that it's indeed a valid license. Hence the reason for the hefty fines if caught without the IDP.