Joint Implementation (JI) is established under Article 6 of the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC). JI enables Annex 1 countries (developed countries and economies in transition) to undertake cross-border investments in projects aimed at reducing greenhouse gas emissions.

The investor country (or a private actor in that country) provides financial and/or technical assistance to achieve cost-effective greenhouse gas emission reductions in a host country in exchange for emission reduction units (ERUs) or "carbon credits". These credits can then be applied by the investor country toward meeting its obligations under the Protocol.

JI is central to the Japanese strategy for implementing the Protocol and most Annex 1 countries will seize the opportunities which exist in Central and Eastern Europe to invest in more efficient industrial power plants to achieve global reductions of CO2. In order to develop an operational regime for JI, the Conference of the Parties (COP) decided in 1995 to launch a pilot phase for "activities implemented jointly" (AIJ).