When IPv4 became a standard in 1980, its 32-bit address field created a theoretical maximum of approximately 4.29 billion addresses (232). IPv4 was originally conceived as an experiment, and not for a practical implementation, so 4.29 billion was considered to be an inexhaustible amount. But with the growth of the Internet, and the need for individuals and companies to require multiple addresses - your home PC, your cell phone, your tablet, your PC at work/school, your Internet-aware appliances - you can see that something larger than 32-bit address fields would be required. In 1993, the Internet Engineering Task Force (IETF) formed a working group called the IP Next Generation working group.
In 1994 the IETF recommended an address size of 128 bits. While many people think that IPv6 is just a way to create more addresses, there are actually many enhancements that make IPv6 a superior choice to IPv4. Again, I recommend Rick Graziani’s IPv6 Fundamentals book as a must-have on your bookshelf for working with IPv6.