"The familiar IP addresses that are assigned to practically every device that can access the Internet— computers, smartphones, cameras—follow the IPv4 naming scheme which was developed in 1977. The 32-bit system, which follows the xxx.xxx.xxx.xxx pattern, with each set of numbers ranging from 0 to 254, is capable of generation up to 4.3 billion possible addresses.

Vint Cerf, Google’s current chief Internet evangelist and the “father of the Internet,” has said in previous interviews that he thought 4.3 billion IP addresses was more than enough. With the explosive growth in Internet and the potential of having practically everything connected to the Internet, such as refrigerators sending out alerts when running low on milk and cars that double as wireless hotspots, 4.3 billion sounds quite minuscule.

As a replacement scheme, IPv6 has a staggeringly large number of addresses: 340 undecillion. (That's 340 followed by 36 zeros).
The catch, really, is that while IPv4 systems and IPv6 systems can run in parallel, the newer standard is not backwards-compatible. A user on the IPv6 network with an IPv6 address is limited to accessing Websites and services that also have an IPv6 address. The IPv4 address space, which at the moment consists of most of the Internet, becomes inaccessible. Over the years, many ISPs and network providers have come up with IPv6-to-IPv4 tunnels, where the IPv6 traffic is wrapped to look like IPv4 traffic to access the Internet.

Some companies, including Google and Netflix, actually have IPv6-compliant sites, and are readily available to users regardless of which address space they are on.
More companies committing to making their services available on IPv6, means users won't have to worry about complicated setup or configuration to get the tunnels working. They would just plug in their network devices, and surf without worrying about what networking technology they are using."

http://www.pcmag.com/article2/0,2817,2405283,00.asp