Proxy servers are intermediary systems that sit between clients and destination servers, forwarding requests and responses while enabling features like anonymity, caching, security, load balancing, and content filtering. They operate at various layers of the network stack — from Layer 4 (TCP/UDP) transport proxies to Layer 7 (HTTP/HTTPS) application proxies — and serve critical roles in enterprise networks, CDNs, web scraping, privacy protection, and modern microservices architectures. Understanding proxy types, protocols (HTTP, SOCKS, CONNECT), configuration patterns (forward vs. reverse), and operational concerns (authentication, caching, SSL termination, load balancing algorithms) is essential for anyone building, securing, or scaling networked applications.