The Regional Internet Registries have each contributed equally to the formation of the ASO, by way of a Memorandum of Understanding signed on 18 October 1999. Each RIR is responsible for managing Internet Protocol (IP) address space in their own region.

A new Memorandum of Understanding between ICANN and the Number Resource Organization, on behalf of the Regional Internet Registries, was signed on 21 October 2004 at ARIN XIV in Reston, Virginia.

AFRINIC
AFRINIC
Region: Africa region

APNIC
APNIC
Region: Asia and Pacific region

ARIN
ARIN
Region: Canada, many Caribbean and North Atlantic islands, and the United States

 LACNIC
LACNIC
Region: Latin America and parts of the Caribbean

 RIPE NCC
RIPE NCC
Region: Europe, the Middle East and parts of Central Asia