“Render unto Caesar what is Caesar’s”? In many European countries, religion comes at a price: If you want the services of a religious community — for marriages, burial, and other activities — you pay a tax. (In Germany, for example, there is an 8 percent surcharge on your income-tax bill.) A very nice Finnish study by Teemu Lyytikäinen and Torsten Santavirta, “The Effect of Church Tax on Church Membership” (Journal of Population Economics, forthcoming), uses this institution to examine the demand curve for religion. The price elasticity of demand is fairly small—not more than 0.05—but that is partly because until 2003, Finland made it difficult to opt out of a religious community (and opt out of paying the tax). Not surprisingly, once the transactions costs of tax avoidance were reduced, the elasticity of demand appears to have risen.