At present, certified emission reductions (CERs) are not the only one type of carbon credit participating in the world’s carbon market. In fact, CERs forms only a small fraction of the credits being traded and exchanged globally. The Kyoto Protocol originates different types of carbon credits, such as assigned amount of units (AAUs), removal units (RMUs), emission reduction units (ERUs) and certified emission reductions (CERs). The following gives a broad overview how Annex I and non-Annex I Parties may involve in an exchange or purchase of different categories of carbon credits.