On January 1, 2008, the cities of Berlin, Cologne and Hannover introduced low emission zones in their city centers to mitigate air pollution caused by motor vehicles. In the meantime, other German cities followed the example. Low emission zones are identified by traffic signs and additional road signs. As a result of this ordinance all vehicles have to be marked with an "Emission Badge" (Umweltplakette), a sticker which should be displayed on the windshield inside the vehicle. Stickers are valid for all low emission zones in any city in Germany.

How to get an "Emission Badge" for your car?

When driving a rental car, the car rental companies usually provide vehicles that are equipped with all necessary stickers and permits meeting the latest standards required by law.
To obtain an Emission Badge for private vehicles, the only item required is a vehicle registration document (V5) and the vehicle itself. Badges are available from a wide range of suppliers including repair centers, car dealers, vehicle inspection (TÜV) stations and vehicle licensing offices. Emission Badges can also be purchased online before traveling to Germany from the TÜV. Prices can vary from €5 to €10 excluding shipping. Any Emission Badge issued is valid for the entire life of the vehicle and throughout Germany.

For non-German registered vehicles, classification depends on:

 a.) date of registration
 b.) definition of vehicle
 c.) gasoline or diesel

Emission  Standard	Initial Registration	Badge required
gasoline	before 01/01/1993	No Badge (Euro I)
gasoline	after 01/01/2021	Green (Euro IV)
diesel	before 01/01/2021	No Badge (Euro I)
diesel	from 01/01/2021 - 12/31/2000	Red (Euro II)
diesel	from 01/01/2021 - 12/31/2005	Yellow (Euro III)
diesel	from 01/01/2021	Green (Euro IV)

The cities participating in the Enviromental Green Zone scheme are:

Up to 2009:
Berlin, Cologne, Dortmund, Frankfurt am Main, Hannover, Ilsfeld, Leonberg, Ludwigsburg, Mannheim, Munich, Nuremberg, Reutlingen, Stuttgart, Schwäbisch-Gmünd, Tübingen

Starting January 2010:
Dresden, Freiburg, Heidelberg, Karlsruhe, Mühlacker, Osnabrück, Pforzheim, Pleidelsheim

Dates TBA.:
Augsburg, Braunschweig, Darmstadt, Gera, Jena,  Leipzig, Magdeburg, Münster, Neu-Ulm, Pfinztal, Regensburg, Greater Ruhr district

From 2010, it is likely that only vehicles with a green or yellow "Emission Badge" will be allowed to enter a city center, although this may vary and in some cities the timing of period and color may be different.

Will my vehicle be examined when applying for an Emission Badge?
Your vehicle will be checked by an engineer to establish verification of the age and type of engine.

Which vehicles will not be able to claim a badge?
Vehicles without a catalytic converter or a particulate filter.

What do the color categories represent?
The four color categories are directly linked to the European Emission Standards. These are sets of requirements defining the acceptable limits for exhaust emissions of new vehicles sold in EU member states. Euro 2 is Red, Euro 3 Yellow and Euro 4 Green. Petrol vehicles with a catalytic converter are always categorized Euro 4 and will automatically be entitled to a green badge.
 
Where do I attach the sticker?
Attach the sticker to the windshield so that it can easily be seen from the front, but don't have it block the view of the driver. It is best to do this from the inside on the passenger side, at the bottom right-hand corner.

Are there any vehicles which do not require a badge?
Mopeds, motorcycles, machinery (excavators), ambulances and original vintage cars over 30 years old . All other vehicles including cars, SUVs, vans, coaches and HGVs will have to display an Emission Badge. 

What can I do if a badge is refused?
Failed, red or orange badge holders are encouraged to upgrade their vehicles with a catalytic converter, or for diesel engines a particulate filter. Vehicles fitted with such filters can reduce the toxicity of emissions or soot from exhaust by 85%-100%. Most upgraded vehicles will be able to claim a green badge which is necessary for entering a green zone in 2010.

What happens if I drive in a low emission zone without a sticker?
This is considered a regulatory offence and results in a fine of €40. If you hold a German drivers' license you will additionally incur 1 penalty point, which will be registered at the Federal Motor Transport Authority (equivalent to DMV).