|aero||the air transport industry.|
|arpa||reserved exclusively to support operationally-critical infrastructural identifier spaces as advised by the Internet Architecture Board|
|asia||companies. organisations and individuals in the Asia-Pacific region|
|com||commercial organizations, but unrestricted|
|edu||post-secondary educational establishments|
|gov||government entities within the United States at the federal, state, and local levels|
|info||informational sites, but unrestricted|
|int||international organizations established by treaty|
|mil||the U.S. military|
|mobi||sites catering to mobile devices|
|name||families and individuals|
|net||originally for network infrastructures, now unrestricted|
|org||originally for organizations not clearly falling within the other gTLDs, now unrestricted|
|tel||services involving connections between the telephone network and the Internet (added March 2, 2007)|
|travel||travel agents, airlines, hoteliers, tourism bureaus, etc.|
Overall, IANA currently distinguishes the following groups of top-level domains:
The core group of generic top-level domains consists of the com, info, net, and org domains. In addition, the domains biz, name, and pro are also considered generic, however, these are designated as restricted, because registrations within them require proof of eligibility within the guidelines set for each.
Historically, the group of generic top-level domains included domains, created in the early development of the domain name system, that are now sponsored by designated agencies or organizations and are restricted to specific types of registrants. Thus, domains edu, gov, int, and mil are now considered sponsored top-level domains, much like the many newly created themed domain names (e.g., jobs). The entire group of domains that do not have a geographic or country designation (see country-code top-level domain) is still often referred to by the term generic TLDs.
The initial set of top-level domains, defined by RFC 920 in October 1984, was a set of "general purpose domains": com, edu, gov, mil, org. The net domain was added with the first implementation of these domains. The com, net, and org TLDs, despite their originally specific goals, are now open for use for any purpose.
In November 1988, another TLD was introduced, int. This TLD was introduced in response to NATO's request for a domain name which adequately reflected its character as an international organization. It was also originally planned to be used for some Internet infrastructure databases, such as ip6.int, the IPv6 equivalent of in-addr.arpa. However, in May 2000, the Internet Architecture Board proposed to exclude infrastructure databases from the int domain. All new databases of this type would be created in arpa (a legacy domain from the conversion of ARPANET), and existing usage would move to arpa wherever feasible, which led to the use of ip6.arpa for IPv6 reverse lookups.
By the mid-1990s there was discussion of introduction of more TLDs. Jon Postel, as head of IANA, invited applications from interested parties. In early 1995, Postel created "Draft Postel", an Internet draft containing the procedures to create new domain name registries and new TLDs. Draft Postel created a number of small committees to approve the new TLDs. Because of the increasing interest, a number of large organizations took over the process under the Internet Society's umbrella. This second attempt involved setting up a temporary organization called the International Ad Hoc Committee (IAHC). On February 4, 1997, the IAHC issued a report ignoring the Draft Postel recommendations and instead recommended the introduction of seven new TLDs (arts, firm, info, nom, rec, store, and web). However, these proposals were abandoned after the U.S. government intervened.
In September 1998, the Internet Corporation for Assigned Names and Numbers (ICANN) was created to take over the task of managing domain names. After a call for proposals (August 15, 2000) and a brief period of public consultation, ICANN announced on November 16, 2000 its selection of the following seven new TLDs: aero, biz, coop, info, museum, name, pro.
Biz, info, and museum were activated in June 2001, name and coop in January 2002, pro in May 2002, and aero later in 2002. pro became a gTLD in May 2002, but did not become fully operational until June 2004.
ICANN added further TLDs, starting with a set of sponsored top-level domains. The application period for these was from 15 December 2003 until 16 March 2004, and resulted in ten applications. As of June 2005, ICANN had announced the approval of several new TLDs: cat, jobs, mobi, tel, travel.
On 26 June 2008, during the 32nd International Public ICANN Meeting in Paris, ICANN started a new process of TLD naming policy to take a "significant step forward on the introduction of new generic top-level domains." This program envisions the availability of many new or already proposed domains, as well a new application and implementation process.  Observers believed that the new rules could result in hundreds of new gTLDs to be registered.
Unrestricted generic top-level domains are those domains that are available for registrations by any person or organization for any use. The prominent gTLDs in this group are com, net, org, and info. However, info was the only of these, and the first, that was explicitly chartered as unrestricted. The others initially had a specific target audience, however, due to lack of enforcement, acquired the unrestricted character which was later grandfathered.
The term sponsored top-level domain is derived from the fact that these domains are based on theme concepts proposed by private agencies or organizations that establish and enforce rules restricting the eligibility of registrants to use the TLD. For example, the aero TLD is sponsored by the Société Internationale de Télécommunications Aéronautiques, which limits registrations to members of the air-transport industry.
A geographic TLD (or GeoTLD) is a generic top-level domain using the name of or invoking an association with a geographical, geopolitical, ethnic, linguistic or cultural community. As of 2009, only two GeoTLDs existed: the sponsored domains cat, for the Catalan language and culture, and asia, but many others have been proposed (see also proposed top-level domain).
The introduction of several generic top-level domains over the years has not stopped the demand for more gTLDs and ICANN has received many proposals for establishment of new top-level domains. Proponents have argued for a variety of models ranging from adoption of policies for unrestricted gTLDs (see above) to chartered gTLDs for specialized uses by specialized organizations.
A new initiative started in 2008, foresees a stringent application process for new domains that adhere to a restricted naming policy for open gTLDs, community-based domains, and internationalized domain names (IDNs). According to a guidebook published by ICANN, a community-based gTLD is "a gTLD that is operated for the benefit of a defined community consisting of a restricted population." All other domains fall under the category open gTLD', which "is one that can be used for any purpose consistent with the requirements of the application and evaluation criteria, and with the registry agreement. An open gTLD may or may not have a formal relationship with an exclusive registrant or user population. It may or may not employ eligibility or use restrictions."
The establishment of new gTLDs under this program requires the operation of a domain registry and a demonstration of technical and financial capacity for such operations and the management of registrar relationships.
|.aero||the air transport industry.|
|.arpa||reserved exclusively to support operationally-critical infrastructural identifier spaces as advised by the Internet Architecture Board|
|.asia||companies. organisations and individuals in the Asia-Pacific region|
|.com||commercial organizations, but unrestricted|
|.edu||post-secondary educational establishments|
|.gov||government entities within the United States at the federal, state, and local levels|
|.info||informational sites, but unrestricted|
|.int||international organizations established by treaty|
|.mil||the U.S. military|
|.mobi||sites catering to mobile devices|
|.name||families and individuals|
|.net||originally for network infrastructures, now unrestricted|
|.org||originally for organizations not clearly falling within the other gTLDs, now unrestricted|
|.tel||services involving connections between the telephone network and the Internet (added March 2, 2007)|
|.travel||travel agents, airlines, hoteliers, tourism bureaus, etc.|
A generic top-level domain (gTLD) is one category of internet domain with (TLDs) maintained by the Internet Assigned Numbers Authority (IANA) for use on the Internet.
Now, IANA diferenting next groups of Inttop-level domain: