Development banks had almost no involvement in the field of international health just a few decades ago, but today they shape the lives of millions of people by setting global health priorities and implementing health programs. In the context of neoliberal governance, “innovative finance,” and the shift from international to global health, key actors and approaches in the field have shifted, and what counts as relevant expertise in global health has also been called into question. This dissertation examines relationships of power and knowledge in the health work of development banks—examining what comes to count as relevant knowledge, who gets to use it, and with what social and political consequences. It does so by bringing together ethnographic research on two development bank-coordinated projects in Guyana with interview and archival research at the headquarters of the banks that finance and oversee these projects: the Inter-American Development Bank and the World Bank. How do these international financial institutions investigate and understand health problems and implement solutions? What kinds of knowledge and values become influential as bank staff and consultants negotiate with Guyanese healthcare workers and government officials as to what problems will receive priority, through which methods, and who will be served? These are questions about the practice of contemporary governance in late neoliberal capitalism, as past international enthusiasm for private management of social welfare has begun to transform. While international financial institutions emphasize the importance of using economic tools and techniques to determine the “best investments” in public health, my research has highlighted the very different ways that economic knowledge comes to be valued across bank networks—even within a single project. Research and operations divisions, for example, have distinct understandings of how tools such as cost-effectiveness analysis ought to be used. And while economic analysis has been surprisingly absent from operational practice, experts in cultural anthropology and indigenous law have played a central role in shaping health projects in Guyana. In the process, their knowledges have become entangled with development bank histories and logics, and even as these institutions attempt to reform themselves, development bank health projects have continued to inscribe state racial codes in the bodies of Guyanese citizens.