Historically, an Internet organization called IANA (Internet Assigned Numbers Authority) was chartered by ISOC to coordinate the assignment of Internet "identifiers" such as domain names, autonomous system numbers, IP address numbers, protocol numbers, and port numbers.

In the early 1990s, IANA coordinated the establishment of the InterNIC (Internet Network Information Center) with funding from the NSF (National Science Foundation). The InterNIC took responsibility for managing the top-level Internet domain names (.com, .org, .net, and so on) and the other Internet identifiers. InterNIC was a collaborative project of AT&T, General Atomics, and NSI (Network Solutions, Inc.). RFC 1400 (Transition and Modernization of the Internet Registration Service, March 1993) describes the services offered by the InterNIC. AT&T managed the InterNIC Directory and Database Services project, NSI managed the Registration Services project (domain registration and IP address allocation), and General Atomics managed the Information Services project, which was dropped from funding in 1995.

By the late 1990s, IANA and the U.S. government felt that the registration services, address allocations, and other functions should be handled by private-sector authorities. In October of 1998, a broad coalition of the Internet's business, technical, academic, and user communities created a nonprofit corporation called ICANN (Internet Corporation for Assigned Names and Numbers) and gave it responsibility for the functions previously managed by IANA. ICANN also coordinates the Internet's root server system and is dedicated to preserving the operational stability of the Internet.

ICANN is officially defined as follows:

A non-profit, international corporation that was formed in September 1998 to take over global responsibility for Internet Protocol (IP) address space allocation, protocol parameter assignment, Domain Name System (DNS) management, and root server system management functions. These services were previously performed under U.S. Government contract by the Internet Assigned Numbers Authority (IANA) and other entities. IANA is now a part of ICANN. Among its duties, ICANN distributes IP address space, and delegates responsibility for further allocation of IP addresses to the Regional Internet Registries (RIRs): ARIN, RIPE, and APNIC. ICANN is also supporting the efforts to form two new RIRs: one in Africa (AFRINIC) and one in the Latin American/Caribbean geographical region (LACNIC). The ICANN has formally recognized three Supporting Organizations tasked with developing and recommending to the ICANN Board substantive policies regarding matters within their subject areas. The Supporting Organizations also each select three Directors to be named to the ICANN Board. The three Supporting Organizations include:

• The Address Supporting Organization (ASO)
• The Domain Name Supporting Organization (DNSO)
• The Protocol Supporting Organization (PSO)

The IANA and ICANN Web addresses are as follows:

With the formation of ICANN, NSI lost the registration services monopoly it had with InterNIC. The for-profit company is now one of many organizations that register domain names. The InterNIC as it was established in 1993 is no longer in service. However, the site still has valuable information, such as a list of registrars. Since the word "InterNIC" is a registered service mark of the U.S. Department of Commerce, NSI no longer uses the name.

Domain name registration may be accomplished through a number of organizations, including NSI. The following Web site provides a directory of accredited registrars:

While ICANN is responsible for IP address allocation policies, the actual management of IP address space is handled by registries. IP addresses are distributed in a hierarchical manner. At the top of the hierarchy is IANA, which allocates blocks of IP addresses to regional Internet registries (RIRs). The regional registries then further allocate blocks of IP addresses to local Internet registries within their geographic regions. Finally, the local registries assign addresses to end users. There are currently three RIRs: