An American driver's license is accepted in the United States and Canada - for all other countries, check with the embassy or consulate of the country you are visiting.

Some countries require an International Driving Permit (IDP) or similar document in addition to your valid driver's license to legally drive in that country. An IDP can be obtained through the American Automobile Touring Alliance (AATA).
Before renting a car, contact the rental car company to learn about local driving and insurance requirements. Road conditions, laws and driving etiquette vary from country to country, so be sure to learn as much as possible from the country's embassy/consulate in the United States, foreign government tourism offices, or from the car rental company in the country you will be driving in. For the most part, your U.S. auto insurance WILL NOT cover you when driving abroad, however it may when you drive in Canada or Mexico (check with your insurance company to find out). Even if your auto insurance does cover you in the country you will be driving in, it may not meet their minimum requirements - you can purchase additional insurance, if necessary. Most car rental companies can provide auto insurance, but in some countries, the required coverage is minimal - you should always consider purchasing insurance coverage equal to your policy at home.

Enjoy exploring and remember, no matter where you are driving, buckle up!