In 2005, the governors of seven Northeastern and mid-Atlantic US states 1 signed a memorandum of understanding (MoU) in which they agreed to establish a regional cap-and-trade scheme for CO2 in the electricity sector. The Model Rule – which provides the framework for the participating states to establish individual CO2 budget trading programmes through statutes or regulations (RGGI 2005) – was signed in 2008; the Regional Greenhouse Gas Initiative (RGGI, pronounced ‘Reggie’) became the first mandatory, market-based programme for reducing CO2 emissions in the US, effective from January 2009 (RGGI 2016a). Maryland, Massachusetts and Rhode Island signed the MoU in 2007, whereas New Jersey withdrew in 2011 (RGGI 2016b). At present there are nine US states participating in this regional emission trading system (ETS).