The 2020 John Bates Clark Medal of the American Economic Association was awarded to Melissa Dell, Professor of Economics at Harvard University, for her path-breaking contributions in political economy, economic history, and economic development. This article summarizes Melissa Dell's work, places it in the context of the broader literature, and emphasizes how, with its data collection, careful empirical implementation, and audacious ambition, it has revolutionized work in political economy and economic history.