The Chapter describes the role of banks’ IRB systems in assessing credit claims as collateral in Eurosystem monetary policy operations. Drawing on the experience of the Bank of Italy, three key insights are presented. First, in a financial system where bank intermediation predominates, IRB systems strengthen the banks’ capacity to mobilize credit claims and diversify credit risk assessment sources, complementing ECAI and central banks’ internal ratings (or ICAS ratings). Second, the regulatory environment for IRB systems is undergoing significant transformation. Their scope is now being somewhat lessened for supervisory purposes—following the entry into force of CRR3—as well as for monetary policy purposes, as the Eurosystem has decided to give priority to ICAS ratings within its collateral framework. Third, in spite of these developments, IRB systems remain crucial for the assessment of SMEs, particularly in jurisdictions and economic sectors not covered by ICASes. IRB systems will ensure collateral availability and support the effective transmission of monetary policy. According to the latest available data for Italy, even after the introduction of ICAS prioritization, IRB systems are the credit assessment source for 35% of the total volume of credit claims pledged as collateral.