In order to reach any location online, users have to type a unique address into their browsers--the domain name. This name is regulated by a not-for-profit corporation called ICANN. ICANN's regulation of domain names helps keeps the Internet secure and stable, and prevents duplication of domains. Knowing about ICANN and its regulations can be a big help for users interested in registering their own domains.
DNS
The domain name system, or DNS, is designed to help humans navigate the Internet. IP addresses--the strings of numbers that identify computers to one another over a network--are hard for people to remember. A domain name is made up of words and letters, and is much simpler to keep track of. These names are made up of two parts: a top-level domain, such as com, org, or net, and a registered domain name, which must be unique.
Administration
ICANN does not control the content of any domain or IP, but it does administrate them. This corporation helps coordinate how domains are supplied to help avoid clashes over the same name, or two people registering one name for two sites. ICANN's administration is international, which allows users to get the same results, no matter where they are in the world.
Structure
The ICANN organization itself is made up of many supporting organizations. They contribute to the corporation's final decisions, and include groups that deal with IP addresses, groups that deal with domain names, and the managers of country-code top-level domains, such as UK or SE. International treaty organizations and national governments, security groups, average users, and root server operators can all be part of ICANN's advisory committees, which provide recommendations, but do not make decisions on their own.
Accountability
ICANN is held accountable according to the laws of the United States, where it is registered as a corporation. The directors are legally responsible for their duties under corporate law. Internal accountability for domain regulation within ICANN comes from the corporate bylaws, its independently nominated board, and its dispute resolution procedures. These bylaws are meant to promote ethical and responsible regulation.
By Country
While ICANN is the top level, international regulator for domain names, individual countries may also have more regulation. For instance, in Sweden, the domain name system is privately held by the II-Stiftelsen foundation, which must follow the ICANN rules, but can also decide whether a name should be registered under the Swedish top-level domain: SE. If a domain is not connected to Sweden, or if it's considered in poor taste, it can be rejected.