IANA (Internet Assigned Numbers Authority) is the agency responsible for assigning numbers for the Internet. IANA was founded by a loosely formed group of computer scientists, headed by Jon Postel, who developed the ARPANET computer network in the early 1970's. ARPANET evolved to become to the Internet, and IANA continued to be the group responsible for assigning Internet numbers: most prominently the assignment of Internet Protocol (IP) numbers. The Internet is, at it's core, based upon packet switching and IP numbers (addresses) assigned to device that connects to the Internet.
As ARPANET expanded to include International nodes - the first nodes (locations) were located in Norway and England (London) - it became obvious that IANA would struggle to administer these regional nodes: due to IANA being based in California, and lacking the regional knowledge and language skills to deal efficiently with international nodes. Therefore, IANA has delegated responsibilities for assigning regional Internet resource numbers - IPv4, IPv6, ASNs - to organisations referred to as Regional Internet Registries (RIRs). IANA provide each RIR with a large block of Internet resource numbers, and the RIR will then split this large block of Internet resource numbers into smaller blocks, and then apportion a block to a national Internet organisation.
IANA also manages the DNS root zone of the Internet. The Domain Name System (DNS) is one of two Internet namespaces: IP numbers being the other. The DNS is administered by thirteen root nameservers: originally root nameservers were based in North America, but, as international Internet usage expanded, some of these root nameservers have been moved to international locations. RIPE NCC, the European Regional Internet Registry (RIR), manages a root nameserver: k.root-servers.net. Therefore, RIRs can manage a range of crucial Internet services; rather than simple assigning smaller IP blocks to national Internet organisations.
Currently, 2014, there are five Regional Internet Registries (RIRs), who also form the Number Resource Organization: