Joint Implementation is one of two offsetting mechanisms under the Kyoto Protocol, along with the Clean Development Mechanism. Both allow for projects that are certified as reducing greenhouse gas (GHG) emissions to issue credits for each tonne of carbon dioxide equivalent (CO2e) abated, which can then be transferred for use in another country. CDM projects are hosted by developing countries, which do not have emission reduction commitments under the Kyoto Protocol, whereas JI projects are hosted by countries with commitments under the Kyoto Protocol.

As of March 2015, almost 872 million Emission Reduction Units (ERUs) had been issued under Joint Implementation (JI). Host countries must cancel one of their emission allowances for every ERU issued, but more than 95% of ERUs were issued by countries with significant surpluses of allowances in the first commitment period of the Kyoto Protocol.

Of the six largest project types, only one – N2O abatement from nitric acid production – had overall high environmental integrity; for the rest, additionality seems unlikely or questionable, or unrealistic assumptions were used that significantly overestimate emission reductions. Overall, 80% of ERUs issued came from project types with questionable or low environmental integrity.

Overall, the use of JI may have enabled global GHG emissions to be about 600 million tCO2e higher than they would have otherwise been.