The History of IP and IPv4 Exhaustion
From ARPANET to the Internet
IP originated in the 1970s ARPANET and IPv4 was standardized in 1981 (RFC 791). Its 4.3 billion addresses seemed inexhaustible at the time.
IANA and the RIRs
Top-level allocation is handled by IANA (under ICANN), which delegates to the five RIRs by region — see IANA and the RIRs.
IPv4 Exhaustion
Explosive Internet growth drained the IANA free pool in February 2011, followed by each RIR. Today addresses change hands on a transfer market.
The Fix
The long-term answer is migration to IPv6. For now, NAT-based sharing and IPv6 dual stack run side by side.