IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses. Because the original Internet architecture had fewer than 4.3 billion addresses available, depletion has been anticipated since the late 1980s when the Internet started experiencing dramatic growth. This depletion is one of the reasons for the development and deployment of its successor protocol, IPv6. IPv4 and IPv6 coexist on the Internet.

The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to end users and local Internet registries, such as Internet service providers. The main market forces that accelerated IPv4 address depletion included the rapidly growing number of Internet users, always-on devices, and mobile devices.

The anticipated shortage has been the driving factor in creating and adopting several new technologies, including network address translation (NAT), Classless Inter-Domain Routing (CIDR) in 1993, and IPv6 in 1998.

The top-level exhaustion occurred on 31 January 2011. All RIRs have exhausted their address pools, except those reserved for IPv6 transition; this occurred on 15 April 2011 for the Asia-Pacific (APNIC), on 10 June 2014 for Latin America and the Caribbean (LACNIC), on 24 September 2015 for North America (ARIN), on 21 April 2017 for Africa (AfriNIC), and on 25 November 2019 for Europe, Middle East and Central Asia (RIPE NCC). These RIRs still allocate recovered addresses or addresses reserved for a special purpose. Individual ISPs still have pools of unassigned IP addresses, and could recycle addresses no longer needed by subscribers.

Vint Cerf co-created TCP/IP thinking it was an experiment, and has admitted he thought 32 bits was enough.

Every node of an Internet Protocol (IP) network, such as a computer, router, or network printer, is assigned an IP address for each network interface, used to locate and identify the node in communications with other nodes on the network. Internet Protocol version 4 provides 2³² (4,294,967,296) addresses. However, large blocks of IPv4 addresses are reserved for special uses and are unavailable for public allocation.

The IPv4 addressing structure provides an insufficient number of publicly routable addresses to provide a distinct address to every Internet device or service. This problem has been mitigated for some time by changes in the address allocation and routing infrastructure of the Internet. The transition from classful network addressing to Classless Inter-Domain Routing delayed the exhaustion of addresses substantially. In addition, network address translation (NAT) permits Internet service providers and enterprises to masquerade private network address space with only one publicly routable IPv4 address on the Internet interface of a main Internet router, instead of allocating a public address to each network device.

While the primary reason for IPv4 address exhaustion is insufficient capacity in the design of the original Internet infrastructure, several additional driving factors have aggravated the shortcomings. Each of them increased the demand on the limited supply of addresses, often in ways unanticipated by the original designers of the network.