This working paper describes the role of state green banks in helping to deploy and commercialize clean energy technologies. Similar to a public-private partnership, state green banks use initial government funding to lever private investment in clean energy and energy efficiency. This paper discusses the purpose, goals, and structure of state green banks, highlighting Connecticut’s Clean Energy Finance and Investment Authority as a case study. It concludes with the strengths and weaknesses of state green banks as a tool to spur the clean energy economy.