This paper describes the relatively new phenomenon of publicly-capitalized green investment banks and examines why they are being created and how they are mobilizing private investment. Following the successful climate change agreement reached in Paris at COP21, attention has shifted to how countries will achieve their planned climate mitigation “contributions” in the short and medium-term, as well as how countries will transition in the longer term to a low-emissions pathway. To achieve these goals, governments need to make full use of their capacity to leverage and unlock much larger flows of private investment in low-carbon infrastructure. To overcome investment barriers and leverage the impact of available public resources, over a dozen national and sub-national governments have created public green investment banks (GIBs) and GIB-like entities in recent years. A GIB is a publicly capitalised entity established specifically to facilitate private investment into domestic low-carbon, climate-resilient (LCR) infrastructure and other green sectors such as water and waste management. Through their interventions and investments, GIBs are demonstrating to private investors that commercially successful investments are possible and happening now.