A domain name registry is a database of all domain names and the associated registrant information in the top level domains of the Domain Name System (DNS) of the Internet that allow third party entities to request administrative control of a domain name. Most registries operate on the top-level and second-level of the DNS. A registry operator, sometimes called a network information center (NIC) maintains all administrative data of the domain and generates a zone files which contains the addresses of the nameservers for each domain. Each registrar is an organization that manages the registration of domain names within the domains for which it is responsible, controls the policies of domain name allocation, and technically operates its domain. It may also fulfill the function of adomain name registrar, or may delegate that function to other entities. Domain names are managed under a hierarchy headed by the Internet Assigned Numbers Authority (IANA), which manages the top of the DNS tree by administrating the data in the root nameservers.
Some name registries are government departments (e.g., the registry for Sri Lanka nic.lk). Some are co-operatives of Internet service providers (such as DENIC) or not-for profit companies (such as Nominet UK). Others operate as commercial organizations, such as the US registry (nic.us).
The allocated and assigned domain names are made available by registries by use of the WHOIS system and via their Domain name servers. Some registries sell the names directly (like SWITCH in Switzerland) and others rely on separate entities to sell them. For example, names in the .com TLD are in some sense sold “wholesale” at a regulated price by VeriSign, and individual domain name registrars sell names “retail” to businesses and consumers.