We quantify the gains from regulating maturity transformation in a model of banks that finance long-term assets with nontradable debt. Banks choose the amount and maturity of their debt by trading off investors’ preferences for short maturities with the risk of systemic crises. Pecuniary externalities make unregulated debt maturities inefficiently short. In calibrating the model to eurozone banking data for 2006, we find that lengthening the average maturity of wholesale debt from 2.8 to 3.3 months would produce welfare gains with a present value of euro 105 billion, while the lengthening induced by the NSFR would be too drastic. Received November 27, 2014; editorial decision November 14, 2016 by Editor Itay Goldstein.

We quantify the gains from regulating maturity transformation in a model of banks that finance long-term assets with nontradable debt. Banks choose the amount and maturity of their debt by trading off investors’preferences for short maturities with the risk of systemic crises. Pecuniary externalities make unregulated debt maturities inefficiently short. In calibrating the model to eurozone banking data for 2006, we find that lengthening the average maturity of wholesale debt from 2.8 to 3.3 months would produce welfare gains with a present value of euro 105 billion, while the lengthening induced by the NSFR would be too drastic.

We analyze optimal cross-country risk sharing and bank capital requirements amid collective moral hazard by governments and banks. Transfers provide insurance but weaken fiscal discipline. Since lenient fiscal policies amplify banks’ risk-shifting, optimal support must be contingent on banking system health. For fiscally weak countries, support is larger in sovereign crises with solvent banks. For fiscally strong countries, support is larger in joint sovereign and bank crises, requiring deposit insurance mutualization. Optimal contracts feature lower capital requirements than without cross-country transfers, raising the cost of joint sovereign and bank crises to strengthen fiscal discipline and enable greater risk sharing.