The paper quantitatively investigates, in general equilibrium, the interaction be-tween the firms ’ choice to operate in the formal or the informal sector and government policy on taxation and enforcement, given a level of regulation. A static version of Ghironi and Melitz’s (2005) industry model is used to show that firms with lower pro-ductivity endogenously choose to operate in the informal sector. I use cross-country data on taxes, measures of informality, and measures of regulation (entry and compli-ance costs, red tape, etc) to back out how high the enforcement levels must be country by country to make the theory match the data. Welfare gains from policy reforms can be fairly large. I find also that welfare gains from reducing regulat...