The distribution of IP addresses is hierarchical. At the top level is The Internet Corporation for Names and Numbers (ICAAN). One of its departments is the Internet Assigned Numbers Authority (IANA). This is the main operator that coordinates and manages the internet as we know it and the numbering rules behind DNS and IP addresses.
IANA distributes large blocks of IP addresses to five continental Regional Internet Registries (RIRs). Next, the RIRs assign smaller IP address blocks to ISPs and other network operators. From there, Internet operators and the ISPs allocate IP addresses to the end-users.