Collective Moral Hazard, Risk Sharing, and Banking Unions*

Abstract 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.