Public banks are an economic and policy tool used by governments around the world for over five centuries that have re-popularized since the 2008 financial crisis for their capacity to lend to developing sectors (e.g. clean energy), support underinvested communities, and provide counter-cyclical financing. Existing research and contemporary policy discourse debates the economic functions of public banks, yet no systematic studies examine what leads governments to form them in the first place, in part due to a lack of data. This paper introduces an original dataset, conceptual framework, and descriptive empirical insights to serve as the basis for future research. I discuss contending definitions of public banks to advance the more targeted conceptualization of ‘government-initiated public banks’, or banks that are formed by governments and remain under government control through ownership and/or management. The dataset includes 1,355 banks and spans 195 countries for the period 1401–2020. Using these data, I test prevailing assumptions suggesting public banks are more likely to form in less developed or more autocratic countries. I show that for the period 1970–2020, public bank formation is instead associated with developed democracies. Descriptive analysis prior to the 1970s further supports a more complex view. These findings help reveal that public banks are not an anachronistic relic of statist development policy, as their formation persists through the neoliberal era, and nor are they a novel policy solution to contemporary challenges, as some recent public policy discourse would suggest. Rather, their historical persistence and recurrent pursuit by governments going back centuries indicate they are a mainstay of government policy; they are an old, novel idea.