An American driver's license is valid in Germany for up to six months. If you plan on staying longer, you will need to acquire a German driver's license.

This requires either simply exchanging your current license for a German one, depending on state of residency, or taking both a written and a driving exam. International Driver's License allows you to travel abroad with confidence. The International Driver Document is recognized worldwide as a valuable document identifying you as a properly licensed resident. No test is required, however, you must have a valid Native Driver's License and be 18 years of age or older to qualify.
    The translation of native Driver's License provided by idlicense.com is certified. The "International Driving License" passport contains pages in 11 foreign languages representing your National Drivers License. This will allow you to drive in almost any country in the world using your International Driving License. The passport of the International Driving Document also contains the list of countries which have signed the "United Nations Convention on Road & Traffic" resolution to accept the International Driving License.  The authorization for the International Driver License has its basis in the United Nations conventions on Road Traffic and Safety held in 1923, 1943, 1949 and 1968, which established standards for the International Driving permit.

When traveling overseas, carry an International Driving Permit,  even if you're not planning to drive. Should you need to communicate with foreign authorities, this recognizable form of identification can help you get on your way more quickly.

Although many countries do not recognize U.S. driver's licenses, most countries accept an International Driving Permit (IDP).  IDPs are honored in more than 150 countries outside the United States. An IDP functions as an official translation of a U.S. driver's license into ten foreign languages.  These licenses are not intended to replace valid U.S. state licenses and should only be used as a supplement to a valid U.S. license.  IDPs are not valid in an individual’s country of residence. Before departure, you can obtain an IDP from an automobile association authorized by the U.S. Department of State to issue IDPs.  Article 24 of the United Nations Convention on Road Traffic (1949) authorizes the U.S. Department of State to empower certain organizations to issue IDPs to those who hold valid U.S. driver’s licenses.  The Department designated the American Automobile Association (AAA) and the American Automobile Touring Alliance as the only authorized distributors of IDPs.