Customizing and Extending SSRS (SQL Server Reporting Services) involves modifying report layouts, functionality, and behavior to meet specific business requirements. It includes designing custom report templates, adding parameters, and enhancing visual elements such as charts and tables. Developers can extend SSRS using custom code, expressions, and external assemblies to implement advanced logic. Integration with external data sources and embedding reports into applications are also common extensions. These capabilities improve reporting flexibility, usability, and business relevance. Customizing and extending SSRS helps organizations deliver tailored, interactive, and data-driven reporting solutions in enterprise environments.