| AS Smedgården | Real estate | 1915 |
| AS Solutions AS | | 2022 |
| AS Sundlandsflaten | Households | 1949 |
| AS Thonning Owesensgt 10 | Households | 1948 |
| AS THS Angellsgt 22 | Real estate | 1957 |
| AS Trondhjems Papir & Papfabrik | Manufacturing | 1909 |
| AS Tonstad Beboertjenester | Administrative & support | 1983 |
| AS Undals Verk | Real estate | 1865 |
| AS Valgrindvegen 5 | Households | 1947 |
| AS Valgrindveien 13 | Households | 1956 |
| AS Viktor Baumannsv 30-36 | Households | 1955 |
| AS Vital | Real estate | 1980 |
| AS Voldsminde IV | Households | 1953 |
| AS Voldsminde V | Households | 1954 |
| AS Voldsminde Vi | Households | 1953 |
| AS Østmarka Boliglag | Households | 1957 |
| Asbjørnsen Holding Trondheim AS | | 2022 |
| Asem Invest AS | | 2024 |
| Asia Norway AS | Wholesale & retail | 2018 |
| Asia-Tropican Food AS | Wholesale & retail | 2009 |
| Asino AS | Professional & scientific | 2023 |
| Asira AS | | 2006 |
| Ask Ventures AS | | 2026 |
| Askara AS | Hospitality | 2023 |
| Askara Group AS | Hospitality | 2025 |
| Askjem Bobilformidling Trøndelag AS | Wholesale & retail | 2024 |
| Asli AS | | 2025 |
| Asolvi AS | Information & communication | 2007 |
| ASP1 Eiendom Og Invest AS | Construction | 2021 |
| ASP1 Holding AS | Construction | 2020 |
| Aspaas Holding AS | Real estate | 2007 |
| Aspekt Mental Helse AS | Health & social care | 2025 |
| Aspen AS | Education | 2025 |
| Aspen Bidco AS | Information & communication | 2019 |
| Aspen Holdco AS | Information & communication | 2019 |
| Aspen Topco AS | Information & communication | 2018 |
| Aspen Wellness AS | Education | 2025 |
| Aspira Invest AS | | 2022 |
| Aspirations AS | Professional & scientific | 2024 |
| Asplem Holding AS | | 2023 |
| Asr Holding AS | Professional & scientific | 2013 |
| Assa Invest AS | Real estate | 2016 |
| Ast Regnskap AS | Professional & scientific | 1997 |
| Asta Klatring AS | Manufacturing | 2016 |
| Astar Consulting AS | Information & communication | 2026 |
| Astar Labs AS | Information & communication | 2023 |
| Astar Technologies AS | Professional & scientific | 2024 |
| Astil Invest AS | | 2018 |
| Astone Holding AS | Financial services | 2011 |
| Astor AS | | 2023 |
| Astor Eiendom AS | Real estate | 1999 |
| Astrid E Kulen AS | Real estate | 2024 |
| Astro PLC AS | Information & communication | 2026 |
| Astrono AS | Information & communication | 2020 |
| Astute Ventures AS | Professional & scientific | 2015 |
| Asuma AS | | 2020 |
| Asylveita 3 AS | Real estate | 2017 |
| Asø AS | | 2021 |
| Asør Eiendom AS | Real estate | 2023 |
| At Rørservice AS | Construction | 2014 |
| Ataata AS | Agriculture & fishing | 2025 |
| Atb AS | Public administration | 2009 |
| Atbrox AS | Information & communication | 2004 |
| Ate Invest AS | Financial services | 2012 |
| Atek Eiendom AS | Real estate | 2014 |
| Atelier Gullvåg AS | Real estate | 2006 |
| Atelier Ilsvika SA | Real estate | 2007 |
| Athene Utvikling AS | Professional & scientific | 2026 |
| Athina Frisørene AS | Other services | 2006 |
| Athom AS | Wholesale & retail | 2023 |
| Athos Holding AS | Real estate | 1994 |
| Athos Tambartun Bolig AS | Real estate | 2019 |
| Atl Bygg AS | Construction | 2023 |
| Atla Lasers AS | Manufacturing | 2012 |
| Atlanten Panorama AS | Real estate | 2021 |
| Atlantis Opplevelser AS | Education | 2024 |
| Atlas Eierskap AS | | 2025 |
| Atlas Invest AS | Real estate | 2006 |
| Atlas Next AS | | 2020 |
| Atlasen Invest AS | | 2021 |
| Atlet Eiendom AS | | 2005 |
| Atma Da | Wholesale & retail | 2001 |
| Atmos Kunst SA | Wholesale & retail | 2025 |
| Atoli AS | Financial services | 2005 |
| Atsentia AS | Information & communication | 2025 |
| Atva AS | | 2025 |
| Audacter Holding AS | Financial services | 2011 |
| Audiograf Midt Norge AS | Health & social care | 2006 |
| Audioplus Trondheim AS | Health & social care | 2018 |
| Audiot AS | | 2018 |
| Auds Foredrag.No AS | Education | 2012 |
| Audun Nåvik Rosvold AS | Professional & scientific | 2019 |
| Augustus Holding AS | Financial services | 2005 |
| Auka Bygg Og Eiendom AS | Construction | 2017 |
| Auki-X AS | Professional & scientific | 2022 |
| Auko AS | Real estate | 2019 |
| Auli Nærsenter Eiendom AS | Real estate | 2007 |
| Aunaas Invest AS | | 2018 |
| Aune Teknikkservice AS | Professional & scientific | 2025 |
| Auneco AS | Real estate | 2024 |