This chapter offers an assessment of the life and thought of Paul Rosenstein-Rodan, a pioneer of development economics and one of the first proponents of both the “Big Push” and “balanced growth” theories, with a particular emphasis on his years at MIT (1952–1968). The chapter shows Rosenstein-Rodan’s central role in two critical junctures in the history of development economics, namely, the birth of the discipline in the late 1940s, and its decline approximately a quarter of a century later. Rosenstein-Rodan was a fundamental player in both instances. Through the lens of his experiences, it is possible to understand the eclectic beginnings of development economics and the role that MIT’s Center for International Studies (Cenis)—and Rosenstein-Rodan as one of its leading members—had in it. His career epitomises the arc of development economics, casting new light on the debates and practices that shaped the discipline during its rise, and on the unresolved issues that help explain its decline.