This article is from the Europe FAQ, by Yves Bellefeuille firstname.lastname@example.org with help from Martin Rich M.G.Rich@city.ac.uk.
If you don't have a driver's licence from a European Union (EU) country,
it's strongly recommended that you get an International Driver's Licence
(IDL), whether or not it's strictly required legally. In the USA,
contact the AAA, even if you're not a member. The cost is $ 10 and
you'll need a passport-size photo. In Canada, contact the CAA. You must
carry both the IDL and the licence from your own country.
Ignore posts from other firms claiming to offer IDLs. These are not
legitimate and aren't legally valid. In particular, you can only obtain
an IDL if you have a valid licence in your own country.