Clean Development Mechanism
Credits generated under the Clean Development Mechanism are called Certified Emission Reductions (CERs). A company can earn CERs in the same way as ERUs with the difference that CERs only can be earned by realising emission-reduction projects in developing countries.

Emission trading
Since January 2005 large companies in the EU are bound to emission ceilings. If they cannot reduce their emission sufficiently, they can buy ERUs (after 2008) and CERs, or emission rights from other companies. Also governments with emission targets under the Kyoto Protocol can buy or sell carbon credits.