The optimal inflation tax is computed in monetary models where money is costly to supply.
The models are simple general equilibrium models with money in the utility function or a
transactions technology. The inflation tax is a means of raising taxes to finance exogenous
government expenditures. The alternative means of revenue are also distortionary. The main
point of this article is to show that the robustness of the optimality of the Friedman rule, of a
zero nominal interest rate, resides in the assumption that money is produced at zero cost.