This site is a reference for IPv4 and IPv6
The Internet Protocol (IP) currently resides at v4 and is moving towards v6 - and has been for decades. IP is the principal communications protocol for interconnected devices and established the Internet. IP has the tasks of delivering packets from the source to a host destination. At the current rate IPv6 will be fully implemented by 2148. The reasons for the slow gradual adoption is associated with expensive transistioning costs.
Worth Knowing about IPv4
The Internet is running out of IPv4 addresses and have been for decades. To combat this decade old problem IPv6 was introduced back in 1995. IPv4 has a maximum of 32^2 (32-bit) addresses (approximately 4 billion) and as you know we are about 6 billion people on the Earth.
With the introduction of IPv6 the address-space grew by an ufathomable amount and will properly be around when we reach the status of a fully intergalactive species. The address space of IPv6 is 128-bit; don't get fooled by the 4x - that is around 340 trillion trillion trillion IP addresses (1,329,227,995,784,910,000,000,000,000,000,000,000) which is among other things, one of the reasons IPv6 addresses uses base-16 (hex notation).