AbstractWe analyze the impact of the countercyclical capital buffers held by banks on the supply of credit to firms and their subsequent performance. Countercyclical 'dynamic' provisioning that is unrelated to specific loan losses was introduced in Spain in 2000, and modified in 2005 and 2008. These policy experiments which entailed bank-specific shocks to capital buffers, combined with the financial crisis that shocked banks according to their available pre-crisis buffers, underpin our identification strategy. Our estimates from comprehensive bank-, firm-, loan-, and loan application-level data suggest that countercyclical capital buffers help smooth credit supply cycles and in bad times have positive effects on firm credit availability, assets, employment and survival. Our findings therefore hold important implications for theory and macroprudential policy.