We study three models in which public goods are supplied by
 private contributions. In the first model studied, tax-financed
 government subsidies to private contributions are shown to increase
 the total supply of public goods. There is a surprisingly decisive
 comparative statics result (with a nice proof) that if public goods
 and private goods are both normal goods, then increases in the
 subsidy rate necessarily increase the equilibrium supply of public
 goods. Two other models are studied, in which small changes in tax
 rates and government provision of public goods are neutralized in
 equilibrium by offsetting changes in private contributions. We
 explain the differences in these models that lead to opposing
 conclusions.