|Introduced||19 December 1997|
|TLD type||Country code top-level domain|
|Registry||Ascension Island Network Information Centre (run by Internet Computer Bureau)|
|Sponsor||Cable and Wireless (Ascension Island)|
|Intended use||Entities connected with Saint Helena, Ascension and Tristan da Cunha|
|Actual use||Various uses, sometimes connected to education and academia; a few sites actually on Ascension Island|
|Registration restrictions||2nd-level registrant must have professional or academic qualification; 3rd level registrant must be resident on Ascension Island|
|Structure||Registrations are taken directly at the second level or at third level beneath various 2nd-level labels|
|Documents||Terms & Conditions; Rules|
|Dispute policies||Dispute Resolution Policy|
The .ac top-level domain is the Internet country code (ccTLD) for Saint Helena, Ascension and Tristan da Cunha, used primarily for Ascension Island (Saint Helena has its own ccTLD, .sh). It is administered by NIC.AC, a subsidiary of the Internet Computer Bureau based in the United Kingdom.
Registration for the domain is open to anyone. The registry accepts registrations of internationalized domain names.
The domain is marketed by some domain-brokers as a domain for the city of Aachen, Germany, after the automotive license plate designation ("AC") for the city.
Due to its similarity to the .ac ("academic") second-level domain that exists under some country code top-level domains, some educational institutions also register under the .ac top-level domain: