Mykonos

You can normally rent a car, ATV or motorbike just by showing your passport and a current drivers license. No problem.

BUT....................
If you get in an accident and dont' have the IDP you'll be in serious trouble with the Greek Police. Greek Law requires it and if you can't produce it you could possibly be detained until you come up with the cash to pay for any and all damages to the vehicles involved regardless of whose fault it is and whether or not the damages were pre-existing (especially if the other car belongs to a local seizing the opportunity to play the system!)

AND...................
Your insurance will be invalidated because technically you will have been driving illegally.
And in that regard I also encourage you to take out the local insurance offered when you pick up the car, as much coverage as you can get. Don't rely on the automatic insurance your credit card claims to provide you. You'll be in a foreign country and there won't be a claims adjustor handy.

Just as important: Don't take "No Problem" as a substitute for indicating on the rental acceptance form every little scratch, dent, tear, stain, crack and missing part on the vehicle, inside and out and underneath. Take photos to back up your inspection.

Yes, be VERY sure to check, and check the exclusions while you're at it.

Hi Brittany - Steve is right and wrong at the same time. IDP's certainly are good to have and I always take one. And I have never been asked to show it when renting a vehicle. I just returned from Mykonos among many places in the past six weeks and rented a 4 wheeler in the local area down past the windmills and went all around the Island and to Paradise Beach,. Great fun and inexpensive.
As far as the IDP goes - get one at your local AAA office and then you'll be covered for any situation that could arise. Have fun on Mykonos - I'm in the process of renting a shop there since I spend a few months a year on Santorini - Love the Islands - You will too

Greg