Public banks are banks located within the public sphere of a state. They are pervasive, with more than 900 institutions worldwide, and powerful, with tens of trillions in assets. Public banks are neither essentially good nor bad. Rather, they are dynamic institutions, made and remade by contentious social forces. As the first single-authored book on public banks, this timely intervention examines how these institutions can confront the crisis of climate finance and catalyse a green and just transition. The author explores six case studies across the globe, demonstrating that public banks have acquired the representative structures, financial capacity, institutional knowledge, collaborative networks, and geographical reach to tackle decarbonisation, definancialisation, and democratisation. These institutions are not without contradictions, torn as they are between contending public and private interests in class-divided society. Ultimately, social forces and struggles shape how and if public banks serve the public good.