American Registry for Internet Numbers

The American Registry for Internet Numbers (ARIN) was the first regional address registry (RIR) to become operational, absorbing a number of staff members of the worldwide but U.S. government funded Internet Network Information Center (InterNIC). The U.S. government has steadily withdrawn from funding the Internet infrastructure, since the Internet has become truly international. It is a not-for-profit U.S. corporation.

ARIN is a membership organization, with much of its reference material and presentations freely available. It is also a service organization: one does not need to join ARIN before applying for IPv4 address space, Autonomous System numbers, or IPv6 address space. If an organization does obtain addresses directly from ARIN, which will involve an administrative fee, the receiving organization automatically becomes a member.

The relationships between ARIN and ICANN is complex. ICANN allocates large blocks of Internet numbers to the regional internet address registries]] (RIR): ARIN, RIPE, APNIC, LACNIC, and AfriNIC.

Previously, each of these was an Address Supporting Organization to ICANN. Under the current system, each RIR provides members to the ICANN Number Resource Organization (NRO), which, in turn, acts as the ICANN Address Council.