In order to rent a car in Europe, non-Europeans need a valid driver's license from their home state or province.
Austria, Germany and Switzerland also require an International Driving Permit (IDP), which is actually just a translation of the original license from your home country. However, in Germany you don't need an IDP for a license in English. If you plan to drive a lot outside of Germany, you may still want to get an IDP, which is valid in over 150 countries. The minimum age for the IDP is 18. In the US, you can get an IDP for a small fee from most AAA offices or online.
Although the legal driving age is 18, drivers usually must be over 21 (sometimes even older) to rent a car. As of July 1, 2011 foreign drivers must also be at least 18 years of age to drive any car in Germany.Other Requirements
Drivers must carry a warning triangle (Warndreieck) and a first-aid kit in the vehicle (found in the trunk of all rental cars) for use in an emergency.
Since your North American auto insurance is not valid in Europe, be sure you have coverage from the rental agency.
Most rental cars require unleaded (bleifrei) gasoline or diesel fuel (Diesel), much more common in Europe than in the US.Things to check before you leave the rental lot
Every rental vehicle should have a green insurance certificate ('Green Card'). It is important that you have this before you drive off. If you are stopped by the police, travel to a different country, or have an accident, you will need to produce this document. Make sure that the vehicle has all of the required emergency equipment (warning triangle, first aid kit, spare tire, and jack) and a parking disc. Also, verify what type of fuel the vehicle uses - many German cars use diesel, which helpfully is the same word in German. Before venturing out on the road, make sure you know where all the buttons, knobs, and controls are. Take a little test drive around the lot to get a feel for the car. This will allow you to make any necessary discoveries or adjustments before you get out into the foreign driving environment where you will need to concentrate.