In the context of crediting mechanisms for emission reduction projects, methodologies define how to set the crediting baseline, to test additionality, and to monitor and quantify emission reductions. They are therefore crucial for ensuring the environmental integrity of the carbon credits issued. The over 250 methodologies approved under the Clean Development Mechanism (CDM) of the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC) constitute the most important body of knowledge in this regard.