Jointly optimal regulation of bank capital and liquidity

In an economy with financial frictions, banks endogenously choose excessive leverage and maturity mismatch in equilibrium, as they fail to internalize the risk of socially wasteful fire sales. Macroprudential regulators can achieve efficiency with simple linear constraints, which require less information than Pigouvian taxes. The Liquidity Coverage and Net Stable Funding ratios of Basel III can implement efficiency. Additional microprudential regulation of leverage is required when bank failures are socially costly. Micro- and macroprudential rules are imperfect substitutes. Optimally, macroprudential policy reacts to systematic risk and credit conditions over the cycle, while microprudential policy reacts to systematic and idiosyncratic risk