We analyze the classic problem of sustaining trust when cheating and leaving trading partners is easy, and outside enforcement is difficult. We construct equilibria where individuals are loyal to smaller groups – communities – that allow repeated interaction. Hierarchies provide incentives...

This paper develops a fairly general model of platform competition in media markets allowing viewers to use multiple platforms. This leads to a new form of competition between platforms, in which they do not steal viewers from each other, but affect the viewer composition and thereby the...

Payment card networks, such as Visa, require merchants' banks to pay substantial "interchange" fees to cardholders' banks, on a per transaction basis. This paper shows that a network's profit-maximizing fee induces an inefficient price structure, over-subsidizing card usage and over-taxing...

In a payment card association such as Visa, each time a consumer pays by card, the bank of the merchant (acquirer) pays an interchange fee (IF) to the bank of the cardholder (issuer) to carry out the transaction. This paper studies the determinants of socially and privately optimal IFs in a card...