Here is some basic information on the legal requirements for driving in Italy.
Using your US license
Your US driver’s license is valid in Italy for a limited time (typically for short stays). In theory, an International Driver’s Permit is required. This permit is basically just a translation into various language of the material on your license card. It has no validity in its own right. You can get one at a AAA office in the US. Over the last 20 years or so, the IDP has rarely been a hard requirement. However, recently there has been some report of car rental agencies requiring it. If you get particularly unlucky, you might find a policeman who demands that one be shown.
The Patente di Guida
Once you gain residency in Italy, you have one year to obtain an Italian driver’s license. Although the police may not give you trouble for driving on an American license after a year, they are entitled to do so and might well impound your car. (Remember that in Italy, the police are allowed to stop you without cause.) Moreover, if you get into an accident without a valid license, your insurance coverage may be void. Nuff said.
Earning a driver’s license in Italy is a big deal, and is especially challenging for those not fluent in Italian. You must pass both a theory and a practical driving test.
For experienced drivers from the US, the theory test is the biggest hurdle. The test is given only in Italian (or in German or French if you happen to live in a specific provinces adjoining France and Austria). It consists of 40 true/false questions that are often tricky, full of very specific detail, and written in a strange bureaucratic language more akin to a logic exam. You must get 90% correct to pass. Most non-Italian speakers wind up studying for many, many hours to practice for this test. Even Italian speakers find it difficult. After reading the material covered in the exam (a 600-page book), most people take practice exams until they reliably get only one or two wrong. A reasonable estimate is that you might wind up taking 300 practice tests.
Before taking your theory exam, however, you must obtain a medical release from your doctor and also be examined by a doctor qualified to do medical tests for driving. (This latter test is not rigorous, and largely involves the paying of a fee.) NB: If you wear hearing aids, you will be required to provide documentation from an audiologist that your devices work correctly.
In Italy, the DMV is called the Motorizazzione which typically has offices located in or near provincial capitals (and perhaps other places in populous provinces). Don’t expect to just show up and take a theory test. Tests are scheduled ahead of time, typically with large crowds of teenagers and a monitor who acts like a schoolteacher.
After passing your theory exam, you are awarded a foglio rosa, e.g., a learners permit. You now must wait a period of time (a month and a day) before taking your practical exam, and during that time you must accumulate a minimum of 6 hours of practice driving time with an adult who has been licensed for at least 10 years and who is under the age of 60 (under the age of 65 if your car happens to have a passenger-side brake pedal).
By comparison, the practical exam is easy, although that depends entirely on the nature of your examiner who, in addition to judging your driving, is allowed to ask you detailed questions about, for example, the operation of your car or the proper procedures for administering first aid in a road emergency.
There exists a thriving driving school industry in Italy. For many people from the US, it might make sense to contract with a school to take classes, get materials, conduct driving practice, and handle documentation and test setup. It won’t be cheap, of course. Expect to pay on the order of €600 for all of the above. You can, of course, arrange to do these things by yourself and there is no shortage of written an online course material. However, you might find that your practical exam is a bit trickier than if you were under the guidance of a licensed driving instructor.
Immediately after passing your practical exam, you will receive your license. Your license number will have a P at the end because you are now a neo-patentati. Neo-patentati are special in that for the first year, they must drive cars no more powerful than 55kw. Also, for the first three years, such drivers are limited to 100 km/h on the autostrada and a maximum of 90 km/h on other roads. Moreover, penalties for new drivers are double what they are for others, and driving after the consumption of ANY alcohol is prohibited. You may question whether all of these rules are strictly enforced for adult neo-patentati with years of driving experience. YMMV.