A configuration management database (CMDB) is essential in IT service management as it serves as a central repository for information regarding the organization's IT assets and their relationships. It tracks configurations, dependencies, and changes within the IT infrastructure, enabling effective management of services and incident resolution. The CMDB supports decision-making by providing accurate data for impact analysis and helps maintain compliance with regulatory requirements. By enhancing visibility into the IT environment, a CMDB aids in optimizing performance and aligning IT services with business objectives, ultimately improving service delivery.