France has set up specific areas that are passable by vehicles only with an appropriate anti-pollution sticker ("vignette") displayed, known as CRIT’Air.
The sticker must be displayed clearly in the windscreen of your vehicle when in these specific areas, otherwise you could be fined up to €135. The sticker must be obtained before travel and it can be purchased online at a cost of €4.76 including postage. Vehicles registered outside France must also display it.
Make sure to purchase only on the official CRIT'Air website of the French government, which you can find by clicking here, along with useful information on the scheme. To purchase, you will need a legible photo or scan of your registration cert, and up to 10 days for postal delivery. Once acquired, it remains valid for the vehicle as long as the details on it are legible.
The CRIT’Air sticker is classified into 6 categories, each represented by a colour, from the most pollutant vehicles (CRIT'Air 5 = grey), to the most recent and environmentally friendly (green). In some cities, vehicles with higher CRIT'Air stickers will be forbidden from entering.
You can check what classification sticker you need by entering your vehicle details on the French government site here. You will need the vehicle’s engine Euro emission rating, which is usually detailed on your vehicle registration documents, sometimes titled as ‘Exhaust Emissions’. When driving in France, the following signs indicate where the zone starts and finishes:
You can find out more information about what areas CRIT'Air applies to, and what the specific rules are for each location here.