To strengthen the security of travel to the United States under the Visa Waiver Program, requirements to travel visa-free have been enhanced. Nationals of Visa Waiver Program countries will still be eligible to travel without a visa but will have to obtain an approved travel authorization prior to their travel to the United States.
If you are planning to rent a car in the USA, we recommend to bring an international driver's license. This can be obtained at your city's services. It is not mandatory. you can rent a car with your national driver's license, but it is just easier for the rental company or the police if it is an international version, in English.