Rather like a phone number for networks, an IP address is a number used to identify a particular computer or device on a network that uses the Internet Protocol (IP). This network could be within our home or organisation, or part of a much wider network, such as the internet. The most commonly-used version of IP is version 4 (IPv4) which uses 32-bit numbers for addresses, allowing for around four billion unique addresses. This will eventually be superseded by version 6 (IPv6), which uses 128-bit numbers, allowing for up to 2128 unique addresses and expansion of the internet beyond the four billion address limit.