As a network, a payment system is likely to exhibit network externalities and perhaps some public good characteristics. Such properties may be more pronounced in an electronic payment system, because of its greater reliance on communication infrastructures with high fixed and low variable costs, for instance. This paper presents the basic economics of network externalities and reviews some basic principles regarding public goods. It then asks what these phenomena imply about the role of the Federal Reserve in emerging payment systems. The general conclusion is that there is reason to be skeptical that network externalities and public goods will be significant sources of market failure in electronic payment systems. These phenomena, by themselves, give rise to no particular, essential central bank role in these markets.