IPv4 and IPv6 are two different systems for numbering devices on the internet. The main difference is size: IPv4 has room for about 4.3 billion addresses, which ran out years ago, while IPv6 has room for roughly 340 undecillion — a number large enough that it will not run out. Most connections today use both at once, choosing whichever one works for a given website.
What they look like
IPv4 addresses are written as four numbers separated by dots, like 203.0.113.42. IPv6 addresses are longer and written as groups of letters and numbers separated by colons, like 2001:db8:85a3::8a2e:370:7334. That's the only difference you'll ever actually see on this page: two different-looking numbers for the exact same purpose.
Why IPv6 exists
IPv4 was designed in the 1980s, when nobody expected billions of phones, routers and smart devices to eventually need their own address. Once addresses started running out, providers had to get creative — many now share a single IPv4 address across hundreds of customers using a technique called CGNAT, which can cause problems for things like online gaming or hosting a server from home. IPv6 was designed decades later specifically to have enough room that this kind of sharing is never necessary again.
Does it matter which one you use?
For ordinary browsing, no — a website that supports both will look and behave identically either way, and your browser picks automatically. Where it can matter is anything that depends on a direct, unshared connection: some multiplayer games, video calls, and self-hosted services work more reliably over IPv6 because it avoids the address-sharing that IPv4 now often requires. IPv6 is not inherently faster or more secure; it just avoids some of the workarounds IPv4 needs today.
If you only have one of the two
Having only an IPv4 address is extremely common and not a fault of your device — it usually just means your provider hasn't enabled IPv6 for your connection. See why you might not have IPv6 for the details. Having only IPv6 is rare and usually temporary, since almost every website still needs IPv4 to reach everyone.