How do WebSockets work and when would you use them?

WebSockets provide full-duplex, persistent communication over single TCP connection. Starts as HTTP upgrade request, then switches protocol. Unlike HTTP request-response, both sides can send data anytime. Low overhead (no HTTP headers per message). Use for: real-time apps (chat, gaming, live updates), streaming data, collaborative editing. Alternatives: Server-Sent Events (one-way), long polling (compatibility). Consider: connection management, scaling with sticky sessions or pub/sub.