This paper examines a new dataset of laws and practices governing public procurement, as well as procurement outcomes, in 187 countries. The authors measure regulation as restrictions on the discretion of the procuring agents. They find that laws and practices are highly correlated with each other across countries, and better practices are correlated with better outcomes, but laws themselves are not correlated with outcomes. To shed light on this puzzle, they present a model of procurement in which both regulation and public sector capacity determine the efficiency of procurement. In the model, regulation is effective in countries with low public sector capacity and detrimental in countries with high public sector capacity because it inhibits the socially optimal exercise of discretion. The paper finds evidence broadly consistent with this prediction: Regulation of procurement improves outcomes but only in countries with low public sector capacity.