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Tourists may drive in the US for up to a year with a foreign driving licence, provided the issuing country is party to the 1949 Geneva Convention on Road Traffic (see art. 1 and art. 25 para. 1) or to the Convention on the Regulation of Inter-American Automotive Traffic (Washington, 1943); most countries are contracting parties.
If your foreign licence doesn’t contain a photograph or is written in a language other than English, it’s wise (but not mandatory) to obtain an International Driver’s Permit (IDP). Always carry your foreign licence as well as your IDP. Without an IDP it may be necessary to obtain a certified English translation of your foreign driving licence, usually obtainable from your country’s embassy in the US.