On December 20, 2005, seven states announced an agreement to implement the Regional Greenhouse Gas Initiative, as outlined in a Memorandum of Understanding (MOU) which outlines the framework for a Model Rule. The MOU was signed by the Governors of the participating states, including Connecticut, Delaware, Maine, New Hampshire, New Jersey, New York, and Vermont.
In 2006, in response to public comments on the Model Rule, the states agreed to substantive amendments to the MOU. Those amendments were signed by the agency heads of the energy regulatory and environmental agencies in each participating state.
In early 2007, Massachusetts and Rhode Island, which had participated in the early development of RGGI, signed the MOU, as did Maryland later that year. On November 29, 2011 New Jersey withdrew its agreement to the MOU, effective January 1, 2012.