|Introduced||December 19, 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 Ascension Island|
|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.
Use as an abbreviation for "academic"
- Royal Global University, Guwahati in Assam, India
- The University of Kurdistan - Hawler
- Ralston College in Savannah, Georgia, United States
- Faith Mission Bible College in Edinburgh, Scotland
- It is also used for promotion, campaigns, and URL shortening by various parts of the University of Edinburgh, Scotland
- The Mahidol Oxford Tropical Medicine Research Unit (MORU) in Bangkok, Thailand
- INFORM (Information Network Focus on Religious Movements), based at the London School of Economics
- Newcastle University, an online university unconnected with Newcastle University in the United Kingdom or the University of Newcastle, Australia
- Dhaka International University in Dhaka, Bangladesh
- Community of Physics, an institution that works to advance physics education and research in Dhaka, Bangladesh 
- On 10 December 2013, The Pirate Bay switched to an .ac domain.
- .ac is being used by anti-cheat software Easy Anti-Cheat.
- .ac is occasionally used as an abbreviation for activities and/or accommodation by tourism websites.
- "IDN Code Points Policy for the .AC Top Level Domain" (PDF). nic.ac. 2013-05-20. Archived from the original (PDF) on 2014-08-06. Retrieved 2013-05-23.
- "RGU | Royal Global University, Guwahati". Retrieved 2022-08-10.
- "University of Kurdistan Hewlêr". Archived from the original on 2012-10-29. Retrieved 2009-04-01.
- "Collegium Ralstonianum apud Savannenses - New Website Under Construction". Archived from the original on 2019-04-16. Retrieved 2021-03-30.
- "Faith Marketing Business Consulting | Faith Based Marketing". Archived from the original on 2021-01-22. Retrieved 2021-03-30.
- "University of Edinburgh". edin.ac.
- "Home - Mahidol Oxford Tropical Medicine Research Unit". Archived from the original on 2021-03-08. Retrieved 2021-03-30.
- "New Religious Movements - Latest news from Inform | Inform". Archived from the original on 2021-03-09. Retrieved 2021-03-30.
- "Newcastle". Archived from the original on 2019-09-21. Retrieved 2012-01-17.
- "DIU | Dhaka International University". Retrieved 2021-08-04.
- "Community of Physics | To learn, to share". Retrieved 2022-01-07.
- "The Pirate Bay Moves to .AC After Domain Name Seizure". 2013-12-10. Archived from the original on 2013-12-10. Retrieved 2013-12-10.
- "Easy Anti-Cheat". Archived from the original on 2021-02-17. Retrieved 2021-03-28.
- ""Melbourne - Activities & Accommodation"". Archived from the original on 2020-09-22. Retrieved 2021-06-04.