This report aims to provide policy makers with the first comprehensive study of publicly capitalised green investment banks (GIBs), examining the rationales, mandates and financing activities of this relatively new category of public financial institution. It provides a non-prescriptive stock-taking of the diverse ways in which these public institutions are helping to leverage and catalyse private investment in domestic green infrastructure, with a spotlight on energy efficiency projects. Highlighting the role of GIBs within a broader policy framework to mobilise investment, the report also provides practical information to policy makers on how green investment banks are being set up, capitalised and staffed.