| Adtraction Marketing Oy | Helsinki | 2014 |
| Adumion Oy | Paippinen | 2020 |
| Advance Invest Oy | Köyliö | 2009 |
| Advance Team Oy | Lahti | 2001 |
| Advanced Consulting Adco Oy | Espoo | 1998 |
| Advanced Energy Network Oy | Lempäälä | 2008 |
| Advanced Future Oy | Nummela | 2012 |
| Advanced Maintenance Solutions Oy | Rauma | 2023 |
| Advanco Oy | Tampere | 2008 |
| Advanssi Oy | Espoo | 2009 |
| Advanterra Oy | Jorvas | 2024 |
| Advanzit Oy | Lempäälä | 2023 |
| Advatum Ab | Helsinki | 2025 |
| Adventum Oy | Kantvik | 2015 |
| Adventure Advertising Oy | Espoo | 1997 |
| Adventure Club Enterprises Oy | Helsinki | 2014 |
| Adventure Club Helsinki Oy | Helsinki | 2019 |
| Adventurous Ideas Oy | Helsinki | 2017 |
| Advenu Oy | Ojakkala | 2015 |
| Advera Oy | Hämeenlinna | 2020 |
| Adveras Oy | Helsinki | 2021 |
| Adveritates Oy | Lahela | 2019 |
| Advertising KIOSKI Oy | Rovaniemi | 2005 |
| Advertizen Oy | Helsinki | 2020 |
| Advestia Oy | Espoo | 2002 |
| Advetix Oy | Espoo | 2020 |
| AdviZ Oy | Turku | 2015 |
| Advia Oy | Helsinki | 2016 |
| Advice Brand Oy | Helsinki | 2021 |
| Advice Ky markkinointiviestintä | Helsinki | 1985 |
| AdviceHat Finland AB | Helsinki | 2016 |
| AdviceNord Oy | Jorvas | 2025 |
| AdviceTek Oy | Helsinki | 2015 |
| Advicon Oy | Kauniainen | 2003 |
| Advika Oy | Espoo | 2011 |
| Advimar Ab | Pietarsaari | 2008 |
| Advinovum Oy | Turku | 2022 |
| Advio Oy | Kuopio | 2022 |
| Advion Group Oy | Oulu | 2016 |
| Advion Solutions Oy | Nokia | 2009 |
| Advire Oy | Tampere | 2020 |
| Advisari Oy | Salo | 2021 |
| Advisen Oy | Helsinki | 2024 |
| Advisers Tuominen Oy | Hämeenlinna | 1989 |
| Advisio Oy | Kuopio | 2009 |
| Advisiq Oy | Jyväskylä | 2024 |
| Advisium Oy | Espoo | 2024 |
| Advison Solutions Oy | Lahti | 2019 |
| Advisor Finland Pro Oy | Kauniainen | 1985 |
| Advisorium Oy | Helsinki | 2012 |
| Advisorix Oy | Oulu | 2024 |
| Advisory Excellence Oy | Helsinki | 2025 |
| Advisory House Oy | Varkaus | 2000 |
| Advisory Partner Oy | Helsinki | 2025 |
| Advitech Engineering Oy | Tampere | 1997 |
| Advius Oy | Kuopio | 2024 |
| Advizer Oy | Helsinki | 2015 |
| Advoc Consulting Oy | Helsinki | 1992 |
| Advocacy Strategies Oy | Helsinki | 2015 |
| Advocatus Diaboli Oy | Tampere | 2013 |
| Advocatus Euronet Oy | Helsinki | 1995 |
| Advokatbyrå Boucht & Nikula Asianajotoimisto | Vaasa | 1975 |
| Advokatbyrå C. G. Antell Kb | Helsinki | 1989 |
| Advokatbyrå Carlsson Wingert Ab | Mariehamn | 1988 |
| Advokatbyrå Familja Ab - Asianajotoimisto Familja Oy | Espoo | 2020 |
| Advokatbyrå Kim Åstrand Ab | Vaasa | 2014 |
| Advokatbyrå Lena Mitts Ab | Helsinki | 2000 |
| Advokatbyrå MK-Law Ab | Espoo | 2010 |
| Advokatbyrå Näsman & Båsk Ab | Vaasa | 2015 |
| Advokatbyrå Oscar Lindfors Ab | Mariehamn | 2024 |
| Advokatbyrå Peter Ollus Kb | Espoo | 2002 |
| Advokatbyrå Rehn & Co Ab | Helsinki | 2002 |
| Advokatbyrå Reims & Co Ab | Helsinki | 1990 |
| Advokatbyrå Schultz & Köhler Ab | Turku | 1977 |
| Advokatbyrå Sjöblom Ab | Tammisaari | 2023 |
| Advokatbyrå Widman & Co Ab | Mariehamn | 1990 |
| Advokatbyrå Wrede & Co Ab | Helsinki | 1993 |
| Advokatum Oy | Haapaniemi | 2010 |
| Advox Lakitoimisto Bergman Oy | Tornio | 2024 |
| Adweiss Oy | Lohja | 2024 |
| Adwiser Oy | Helsinki | 2020 |
| Adworks Oy Turku | Lieto | 2011 |
| Adwulf avoin yhtiö | Nummela | 2015 |
| Aearis Oy | Helsinki | 2026 |
| Aecor Oy | Helsinki | 2015 |
| Aecorsan JJ Partners Oy | Espoo | 2024 |
| Aedes Oy | Helsinki | 1994 |
| Aedi Oy | Osoite Tuntematon | 2009 |
| Aedon oy | Espoo | 2010 |
| AegeA Oy | Teuva | 1989 |
| Aegia Oy | Espoo | 2021 |
| Aegis Safety Partners Oy | Vantaa | 2026 |
| Aegna Oy | Helsinki | 2008 |
| Aeindri Protocol Finland Oy | Helsinki | 2022 |
| Aejco Oy | Koisjärvi | 2019 |
| Aeko Company Oy | Espoo | 2015 |
| Aekon Oy | Ylöjärvi | 2025 |
| Aellia Finland Oy | Helsinki | 2014 |
| Aena Agency Oy | Helsinki | 2020 |
| Aenaryod Ky | Lappeenranta | 2021 |