A domain name registry is a database of all domain names registered in a top-level domain. A registry operator, also called a network information center (NIC), is the part of the Domain Name System (DNS) of the Internet that keeps the database of domain names, and generates the zone files which convert domain names to IP addresses. Each NIC is an organisation that manages the registration of Domain names within the top-level domains for which it is responsible, controls the policies of domain name allocation, and technically operates its top-level domain. It is potentially distinct from a domain name registrar.
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.
IANA also operates the .int registry for intergovernmental organisations, the .arpa zone for protocol administration purposes, and other critical zones such as root-servers.net.
Country code top-level domains (ccTLD) are delegated by IANA to national registries such as DENIC in Germany and Nominet in the United Kingdom.
Historically, domain name registries operated on a first-come-first-served system of allocation but may reject the allocation of specific domains on the basis of political, religious, historical, legal or cultural reasons.
For example, in the United States, between 1996 and 1998, InterNIC automatically rejected domain name applications based on a list of perceived obscenities.
Registries may also control matters of interest to their local communities: for example, the German, Japanese and Polish registries have introduced internationalized domain names to allow use of local non-ASCII characters.
Domains which are registered with ICANN registrars, generally have to use the Uniform Domain-Name Dispute-Resolution Policy (UDRP), however, Germany's DENIC requires people to use the German civil courts, and Nominet UK deals with Intellectual Property and other disputes through its own dispute resolution service.
Prices of registration
A basic search engine query on the term "domain registration" reveals that prices for domain registration vary widely between each registry.
Domain name registries may also impose a system of third-level domains on users. DENIC, the registry for Germany (.de), does not impose third level domains. AFNIC, the registry for France (.fr), has some third level domains, but not all registrants have to use them, and Nominet UK, the registry for the United Kingdom (.uk), requires all names to have a third level domain (e.g. .co.uk or .org.uk).
Many ccTLDs have moved from compulsory third or fourth-level domain to the availability of registrations of second level domains. Among them are .us (April 2002), .mx (May 2009), and .co (March 2010).
Registrants of second-level domains sometimes act as a registry by offering sub-registrations to their registration. For example, registrations to .fami.ly are offered by the registrant of fami.ly and not by GPTC, the registry for Libya (.ly).