See if they have rental contracts or at least an explanation of contract terms available in English. Also, see if they will have any English speaking counter personnel available to assist you when you arrive. Your personal insurance or credit card coverage may not be valid or acceptable to the rental company, so you may need to purchase extra coverage. Most rental car fleets outside the U.S. are made up of much smaller cars. Many foreign rental fleets have a large percentage of manual transmission automobiles.
Some countries have both a minimum and a maximum rental age.
The American Automobile Association s International Driving Permit web page. This site contains information on how to get an International Driving Permit. This permit, used in conjunction with your valid U.S. driver s license, is valid in 150 countries. Check out the site s IDP FAQ link for further information. This site contains information on traffic codes, road signs, parking, and road vocabulary for those planning on driving in European countries.