Server-Sent Events (SSE) is a web technology designed for unidirectional real-time data streaming from a server to a client over a single, persistent HTTP connection. Developed to overcome the inefficiencies and complexities of earlier polling and Comet techniques, SSE provides a standardized mechanism, primarily via the browser's EventSource API, for scenarios like notifications, live data feeds, and monitoring dashboards. It leverages standard HTTP with a specific text-based text/event-stream format and offers built-in features for reliability, including automatic reconnection and event ID tracking. While simpler than bidirectional protocols like WebSockets, scaling SSE requires managing numerous long-lived connections efficiently, using asynchronous server models, and carefully configuring network intermediaries and load balancers. Advanced considerations include its benefits and limitations over HTTP/2, securing connections with TLS, and handling CORS policies.