Green card - The Green Card system was set up in Europe almost 50 years ago. Its aim is to make it easier for people to drive across Europe without having to stop at each border to arrange insurance in the country they are about to enter.
The green card is not a legal requirement, but is recommended. It can be obtained from your own insurers and is equivalent to insurance in any one of the 43 member countries. Before going abroad in your car, it's always advisable to check exactly what cover your insurers provide and what the procedure would be in the event of an accident.