A Regional Internet Registry (RIR) is an organization that oversees the registration and allocates IP addresses, both IPv4 and IPv6 and autonomous system (Internet) numbers in a certain region of the world. Namely there are currently 5 registries, all overseen by the Internet Assigned Numbers Authority (IANA):

Collectively the RIRs form part of the Number Resource Organization [http://www.nro.net/] formed as a body to represent their collective interests and ensure that policy statements are coordinated globally.

IANA delegates the allocation of IPv4 addresses to RIRs in large chunks (typically /8 =16.7 million addresses or more at a time), and the RIRs then follow their own policies for address allocation. They typically further delegate address assignment to Internet Service Providers in small chunks, with the smallest currently being /22 (=1024).

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