This paper offers a theory to explain cross-national variation in administrative law doctrines and practices. Administrative law regimes vary along three primary dimensions: the scope of delegation to agencies, agencies’ exercise of discretion, and judicial practices of deference to agencies. Working with a principal-agent framework, we show how cross-national differences in institutions’ capacities and the environments they face encourage the adoption of divergent strategies that lead to a variety of distinct, stable, equilibrium outcomes. We apply our model to explain patterns of administrative law in the United States, Germany, France, and Commonwealth jurisdictions.