Driving from France into Germany

We will being doing something similar in June but I thought I had read we needed a Germany decal - not sure how that will work out with our Swiss rental.

You will need to check with your car hire company that you can take it across the border. I have had some rentals that charge more to take the vehicle into a second country, even though there is no physical border.

Two years ago we did the same thing and just drove across the border/Rhine River on the D415.

If you plan to drive into the city of Freiburg itself (or many other cities in Germany), you need to have the Umweltplakette, which is an Emissions-Sticker. I found this site in English about it (a bit out of date, though, the fines and costs are higher now). This site includes some brief information about rental cars and how to go about getting a Umweltplakette for one--they suggest a TÜV inspection centre, though there may be better options (we usually get it either from our city hall or from the dealership/workshop--maybe someone here has experience with this on international rental cars, or maybe there are other threads on the internet elsewhere).

A car rented in Colmar itself may come with the sticker, since there is so much cross-border traffic in the area. But, you would need to check with the rental agency. If not, you risk a fine.

Thanks to all for the info. It looks like Freiburg requires a sticker, so we will have to see about getting one or stay out of the city itself.
Chris