What Is a Top-Level Domain?

A clear explanation of TLDs, the DNS hierarchy, and the main categories.

The short answer

A top-level domain (TLD) is the last segment of a domain name — the part after the final dot. In example.com, the TLD is .com. In example.co.uk, the TLD is .uk (with .co being a second-level domain).

TLDs sit at the top of the Domain Name System (DNS) hierarchy. They are the first stop when a resolver looks up a domain name.

The DNS hierarchy

The DNS is a distributed, hierarchical naming system. From top to bottom:

  1. Root zone — represented by an empty label (the trailing dot in example.com.). Managed by IANA/ICANN.
  2. Top-level domains (TLDs) — .com, .org, .uk, .中国, etc.
  3. Second-level domains — example in example.com.
  4. Subdomains — www, mail, blog, etc.

When you type a domain in a browser, a recursive resolver starts at the root, asks for the TLD's authoritative name servers, then asks those for the second-level domain, and so on.

Main TLD categories

IANA's Root Zone Database index page was redesigned in 2026 and now publishes only three type values. Earlier pages used six. Both are described below so the older terms you may still find in blog posts still make sense.

Generic TLDs (gTLDs)
Open to global registration. Examples: .com, .org, .net,.dev, .app, .biz. In IANA's current taxonomy.gov, .edu, .museum and .aero are also listed here, even though they were historically called sponsored.
Country-code TLDs (ccTLDs)
Two-letter codes from ISO 3166-1. Examples: .uk, .de, .jp,.ai, .io. Each is managed by a national registry with its own rules.
Special-use TLDs
IANA labels .arpa as "Special Use" — it is delegated but reserved for technical infrastructure. Eight further names (.test, .example,.invalid, .localhost, .local, .internal,.alt, .onion) share the label but are not delegatedand never appear in the public DNS.
Internationalized TLDs (IDN TLDs)
A cross-cutting view, not an IANA type: TLDs stored as punycode and displayed in a native script (.中国 → .xn--fiqs8s). Both generic and country-code IDNs exist.

Older IANA pages separated two further groups: Sponsored TLDs (.gov, .edu, .museum, .aero, .post) and Generic Restricted TLDs (.biz, .name, .pro). IANA no longer publishes those labels, so this site does not either — the eligibility rules they described are still set by each registry and are linked from the individual TLD pages.

Who runs the TLD system?

  • IANA (Internet Assigned Numbers Authority) — maintains the authoritative Root Zone Database and coordinates the root zone.
  • ICANN (Internet Corporation for Assigned Names and Numbers) — policy development and oversight of the DNS root.
  • Registry operators — run the authoritative name servers and registration database for a specific TLD (e.g. VeriSign for .com).
  • Registrars — accredited retailers that sell domain registrations to end users.

How many TLDs exist?

As of October 2026, there are over 1,400 delegated TLDs in the IANA root zone. The exact number grows as new gTLDs are delegated and ccTLDs are added or retired.

You can browse the current list on our TLD directory or download the authoritative list from IANA.

Key takeaways

  • A TLD is the highest level in the DNS hierarchy after the root.
  • Every TLD has a registry operator responsible for its technical operation.
  • IANA publishes three type values (Generic, Country Code, Special Use); the older "sponsored" and "generic-restricted" labels are no longer published.
  • The IANA Root Zone Database is the single authoritative source for TLD data.