How Are IP Addresses Assigned?

We don't "own" our IP address—for instance, it's not like a homeowner's address, which is linked to a piece of land and a building on it. Your IP address can change and it's never really tied to your name or address, at least not in a way the public can see it.
But this doesn't mean we can randomly choose any IP address—for instance, like the way you're allowed to choose a username for an email account. Because when it comes to something the size of the Internet—and the complexity and intricate networking involved—that sort of randomness would produce nothing but chaos.
That's why behind the extensive and global yet seemingly simple Internet, there is an order and system that helps keep it working smoothly...even with details as small as our IP address.

Meet IANA.

For networking administrators and those who want to build private home or office networks, there are blocks of private IP addresses that are reserved for special use. But when it comes to the rest of us and our need for global IP addresses, there has to be some sort of ordering scheme to assign IP addresses in a logical, orderly and working fashion.
For the Internet, there is a single, worldwide "allocation" process for this, and it begins with an organization—the Internet Assigned Numbers Authority, or IANA.
IANA, based in the United States, is an Internet-specific organization that gives out (assigns and allocates) IP addresses in a systematic, organized and consistent manner that benefits everyone.
Still, with more than four billion IP addresses assigned worldwide, it's a bit overwhelming for just one single organization to handle, so IANA has some help from other Internet associations.
Part of the IP address allocation process has been simplified by assigning large blocks of IP addresses to Regional Internet Registries (RIR). Each RIR is responsible for managing the IP addresses assigned to their region on behalf of IANA.
There a number of Internet organizations involved with helping to keep the network operating smoothly and efficiently. Each one takes care of one aspect of the Internet and carefully follows policies and procedures (that are set up by other Internet organizations).
IANA and RIRs make sure our IP addresses will work when we need them to work, whatever that IP address at any one time is and wherever we happen to be.