The top-level domains (TLDs) are the highest level of domain names of the Internet. They form the DNS root zone of the hierarchical Domain Name System. Every domain name ends in a top-level or first-level domain label.

When the Domain Name System was created in the 1980s, the domain name space was divided into two main groups of domains. The country code top-level domains (ccTLD) were primarily based on the two-character territory codes of ISO-3166 country abbreviations. In addition, a group of seven generic top-level domains (gTLD) was implemented which represented a set of categories of names and multi-organizations.^[2] These were the domains GOV, EDU, COM, MIL, ORG, NET, and INT.

During the growth of the Internet, it became desirable to create additional generic top-level domains. As of June 2009, there are 20 generic top-level domains and 248 country code top-level domains. In addition, the ARPA domain serves technical purposes in the infrastructure of the Domain Name System.

During the 32nd International Public ICANN Meeting in Paris in 2008, ICANN started a new process of TLD naming policy to take a "significant step forward on the introduction of new generic top-level domains." This program envisions the availability of many new or already proposed domains, as well a new application and implementation process. Observers believed that the new rules could result in hundreds of new top-level domain to be registered.

An annotated list of top-level domains in the root zone database is published at the IANA website at http://www.iana.org/domains/root/db/ and a Wikipedia list exists.