I read this thread (in partial horror) on my mobile phone while I was sitting on a delayed IAD-MUC flight a week ago. It was then, on the plane, that I happened to be thumbing through a guidebook that says "International Driver's Permits are required in Austria." My rental was from MUC, but we were immediately going to cross Austria. Then I thought...what if Germany requires one too?

Anyway, long story short: nobody in Europe, either Hertz or overland border agents, asked for an IDL. I even asked Hertz: "Should I go to ADAC and get one?" (ADAC is the German version of AAA.) The agent just laughed and said don't worry about it. We actually did stop at an ADAC that happened to be at an autobahn rest area and the guy there also said not to worry about it.

At border crossings - both exiting and entering the EU at the Croatian border - they just wanted to see passports, not licenses. (Other threads had indicated that we might need to show insurance paperwork, but they did not ask for that either.)

Of course, getting stopped by a non-English-speaking cop might have been problematic, but that didn't happen. Next time I rent abroad, I'll probably get an IDL since it's easy to do, but one definitely is not needed to rent a car in Germany or to cross into or out of the EU zone.

A friend of ours also there at the same time rented in Austria - the country that the guide book said required the license. He had no problems renting there without an IDL either. In fact, they gave him a Mercedes to drive to Croatia - something I specifically asked Hertz not to do because of a warning I'd seen on the German Hertz site about specific makes/models prohibited from leaving Germany and Austria. He had no troubles.