The Internet Corporation for Assigned Names and Numbers (ICANN) is a US-based not-for-profit public-benefit corporation whose role is to coordinate, at the overall level, the global Internet's systems of unique identifiers, and to ensure the stable and secure operation of these systems. ICANN's main responsibiliy is to coordinate the allocation and assignment of the three sets of unique identifiers for the Internet (also known as 'critical Internet resources': domain names, Internet protocol (IP) addresses and autonomous system numbers, and protocol port and parameter numbers), as well as to facilitate the coordination of the operation and evolution of the Domain Name System (DNS) root name server system.
Until September 2016, ICANN was mandated by the United States Department of Commerce (DoC) to perform the IANA (Internet Assigned Numbers Authority) functions, including globally alocating the IP addresses and other numbering resources to the Regional Internet Registers (RIRs), introducing changes to the main DNS root zone file (the global Internet 'address book’), and managing the .INT top-level domain. Starting October 2016, these functions are performed by ICANN's affiliate Public Technical Identifiers (PTI), following the transition of the IANA functions stewardship from the US government to the global multistakeholder community.
ICANN also has a policy-making function, in that it defines policies for how the 'names and numbers' of the Internet should run. The work moves forward in a style described as the 'bottom-up, consensus-driven, multistakeholder model', through the various supporting organisations and advisory committee that are part of ICANN's structure.