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I have a Russian relative who will be visiting the U.S. for a short time (less than a month) and I would like him to be able to drive my car while he's here.
Will he need an International Driving Permit, or will his license be valid by itself?
(I would appreciate authoritative answers with links to government websites on these points, as my searches didn't turn up anything authoritative. It seems like the license is valid but an IDP is recommended, but it's not clear.)
This is about California specifically if it varies at the state level.