If contracts are costlessly enforcible then insolvency is the only reason for nonrepayment of loans. While some models have examined the borrower's incentive to repay, it has typically been assumed that the penalty suffered by a debtor in default is imposed automatically and without cost to the lender.If in fact invoking a penalty is costly, Pareto-improving loans may be dynamically inconsistent not because of the absence of a sufficiently harsh penalty for default, but because the lender has no incentive actually to implement the penalty in the event of default. In such situations infinitelylived institutions can emerge as banking intermediaries between lenders and borrowers. These institutions, repeatedly involved in lending, have an incentive to enforce contracts that individual lenders lack. They can consequently sustain more lending. For their reputations as enforcers of contracts to have value requires that banks earn strictly positive profits.Maintaining the value of bank equity also provides an incentive for bank owners to invest deposits rather than to use these funds fraudulently.Because of the supernormal profits that banks must earn, an equilibrium that is sustained by bank reputation will not replicate an equilibrium in which loan repayment is automatically guaranteed.