This report gives an overview of the green bank model, existing green banks, and the potential for a federal green bank. Historically, the U.S. has supported the adoption of clean energy technologies by offering incentives, rebates, tax credits, and other forms of subsidies. While these types of support and funding have been effective in improving the economics of clean energy technologies, they are not enough to reach climate goals. According to a Climate Policy Initiative report, to achieve the goals of the Paris Agreement, global supply-side energy generation alone will require $1.6-$3.8 trillion in annual investment between 2016 and 2050. This level of investment is substantially more than the $546 billion that was deployed in 2018. Private capital will need to make up most of this investment, but private investors often perceive this market segment as risky due to its relatively short history and the uncertain future of government subsidies. One solution is developing green banks. Green banks are institutions that finance clean energy and green infrastructure projects in partnership with private lenders. These institutions can help address the financing gap by reducing the risks and administrative burdens for private investors, making it easier for clean energy projects to get financing. Although the green bank model is relatively new, new green financing institutions are being developed across the country, and there are increasing opportunities at the federal level.