We present a model in which setting up and running a regulatory institution takes a fixed cost. As a consequence, the supply of regulation is limited by the extent of the market. We test three implications of this model. First, jurisdictions with larger populations affected by a given regulation are more likely to have it. Second, jurisdictions with lower incremental fixed costs of introducing and ad- ministering new regulations should regulate more. This implies that regulation spreads from higher to lower population jurisdictions, and that jurisdictions that build up transferable regulatory capabilities should regulate more intensely. Consistent with the model, we find that higher population U. S. states have more pages of legislation and adopt particular laws earlier in their history than do smaller states. We also find that the regulation of entry, the regulation of labor, and the military draft are more extensive in countries with larger populations, as well as in civil law countries, where we argue that the incremental fixed costs are lower.