It’s worth remembering that while the internet is not centralised, some aspects of the internet including internet infrastructure must be organised centrally in order for the internet to work smoothly. IANA, the Internet Assigned Numbers Authority was founded by the US government as an organization in 1988. It is now managed by ICANN, the Internet Corporation for Assigned Names and Numbers.
IANA is an essential department of ICANN, it is the authority that allocates IP addresses and domains. IANA also performs technical maintenance of some of the most important rules and structures of the internet. These must be co-ordinated internationally and IANA is the international organisation that co-ordinates it.
The DNS root zone is what helps coordinate communication amongst the millions of internet devices. IANA operates the root DNS zone, which includes all the TLDs – IANA maintains and assigns these domains. It also includes management of the .arpa domain, which is for internal infrastructure, as well as the .int domain which is a TLD used for specific international organisations.
In addition to managing TLDs IANA also manages IP address allocation as well as AS numbers. IANA allocates these to the five RIRs, the Regional Internet Registries. RIRs, in turn, can hand over IP addresses to the Internet Service Providers (ISPs) in their local regions.
Furthermore IANA is also responsible for protocol registries, a database of all the codes which are used by the internet protocols we commonly use.