DNS (Domain Name System) translates human-readable domain names into IP addresses that computers use to communicate. When you type a URL, your browser checks its cache, then the OS cache, before querying a recursive resolver. The resolver contacts root servers, TLD servers, and finally authoritative name servers to find the correct IP address. DNS achieves speed and reliability through caching, anycast networks, redundant servers, GeoDNS, load balancing, and CDN integration. This hierarchical system processes billions of queries daily in milliseconds, making the internet user-friendly while maintaining machine efficiency.