The Clean Development Mechanism (CDM) is an instrument established in the Kyoto Protocol of the United Nations Framework Convention on Climate Change (UNFCCC), designed to reduce greenhouse gas (GHG) emissions and promote sustainable development.[1] This mechanism allows developed countries, which have assumed emissions reduction commitments under the protocol, to implement projects in developing countries aimed at reducing GHG emissions. In exchange, developed countries receive Certificates of Emission Reductions (CERs), each equivalent to one ton of carbon dioxide, which can be traded or used to meet their climate goals.[2][3]​.

The CDM has been applied in sectors such as industrial, energy, forestry, transportation and waste management, contributing to both climate change mitigation and sustainable development in developing countries.[4]​ In addition, it constitutes the main source of financing for the UNFCCC Adaptation Fund, which supports climate change adaptation projects in vulnerable regions. It is considered a pioneering mechanism as it is the first global standardized emissions compensation system based on the market.[5]​.

The Clean Development Mechanism (CDM) was introduced within the framework of the Kyoto Protocol, adopted in 1997 and in force since 2005. This mechanism was part of the so-called flexible mechanisms of the protocol, designed for countries to collaborate in meeting their commitments to reduce greenhouse gas emissions. The main objective of the CDM was to benefit developed and developing countries, promoting sustainable projects in the latter, while the former obtained Emission Reduction Certificates (CER).[6][7]​.

The CDM formally began operating in 2006, and during its first commitment period (2008-2012) it registered more than 1,650 projects. These were expected to generate CER equivalent to more than 2.9 billion tonnes of CO2. However, in its first years, the mechanism produced fewer credits than expected, in part due to a lack of financing and personnel in the supervisory bodies.[2]​.

The design of the CDM faced significant criticism. A major concern was the additionality of emissions reductions, that is, whether projects achieved reductions that would not have been achieved otherwise. Another concern was the possibility that developed countries or companies would promote projects contrary to the development interests of the recipient countries. To address these concerns, the CDM required host countries to confirm that projects contributed to their sustainable development and prohibited credits for activities such as nuclear energy and avoided deforestation.[8]​.