The Domain Name System (DNS) is a distributed database used by computer systems to map between hostnames and IP addresses, and to provide electronic mail routing information. Each site (university department, campus,company, or department within a company, for example) maintains its own database of information and runs a server program that other systems across the Internet can query. The DNS provides the protocol which allows clients and servers to communicate with each other.

This category includes the companies that provide the resources to make this system work, companies that provide the resources to end users for use or resell and sites that discuss issues in the system.