On August 11, 2017, the Massachusetts Department of Environmental Protection (MassDEP) adopted a landmark bundle of regulations for reducing greenhouse gases (GHG). The regulations primarily target carbon dioxide (CO2) emissions associated with electricity generation and supply through a new cap-and-trade program for generators and a “Clean Energy Standard” for retail electricity sellers. The regulations also create new restrictions on methane emissions from natural gas distribution and expand existing restrictions on sulfur hexafluoride (SF6) emissions from electrical system switchgear. Beyond stationary sources, the regulations also address CO 2 emissions from state vehicles and set CO2 reduction targets through 2020 for the state’s transportation system.