| Clickz Systems and Services AS | Information & communication | 2024 |
| CLL Holding AS | Wholesale & retail | 2005 |
| CM Konsultasjon AS | Professional & scientific | 2026 |
| Cobra AS | | 2021 |
| Coco AS | Professional & scientific | 2025 |
| Combiteq AS | Professional & scientific | 2011 |
| Comet Hockey Drift AS | Administrative & support | 2024 |
| Communicate Holding AS | Information & communication | 2003 |
| Communicate Invest AS | Real estate | 2003 |
| Consil Industries AS | Wholesale & retail | 2015 |
| Convia Parterapi AS | Health & social care | 2026 |
| Copernicus AS | Administrative & support | 2019 |
| Core Academy AS | Education | 2025 |
| Cosmion Consulting AS | Professional & scientific | 2026 |
| Ctgs Holding AS | Financial services | 2011 |
| Curtisen AS | Hospitality | 2015 |
| D-M Bygg AS | Construction | 2025 |
| D.O.R.C Scandinavia AB Nuf | Wholesale & retail | 2004 |
| Dag Halvorsen Holding AS | Real estate | 2005 |
| Dag Lillestrand AS | Real estate | 1996 |
| Dag Raa AS | Real estate | 2008 |
| Dag T H Gundersen AS | Professional & scientific | 2018 |
| Dagmar Holding AS | | 2026 |
| Dahles Auto Halden AS | Other services | 2017 |
| Dahlmans AS | Wholesale & retail | 1973 |
| Dalslandskan AS | Professional & scientific | 2023 |
| Damago AS | Real estate | 2021 |
| Daniel Aho | Construction | 2008 |
| Dank I Halden AS | | 2022 |
| Datahjelp Ans | Professional & scientific | 1987 |
| Datakraft Holding AS | Wholesale & retail | 2012 |
| Dataset AS | Information & communication | 2012 |
| Datatjenesten AS | Wholesale & retail | 1989 |
| Dauti AS | Administrative & support | 2017 |
| DB Dominos AS | Hospitality | 2026 |
| De Flon Holding AS | Real estate | 2023 |
| Decna Foods AS | Wholesale & retail | 2014 |
| Dekk Partner Halden AS | Other services | 2018 |
| Delta Sport Ans | | 1994 |
| Den Glade Gribb Ans | Administrative & support | 1994 |
| Dennis Gundersen AS | Information & communication | 2011 |
| Derivat AS | Wholesale & retail | 1976 |
| Derma Vital Ans | Wholesale & retail | 1996 |
| Diamant Wire Teknikk AS | Construction | 1995 |
| Dig Tec AS | Construction | 2018 |
| Digitus Nordic AS | Wholesale & retail | 2012 |
| Dikeveien 37 AS | Real estate | 2022 |
| Din Samtale Viken AS | Health & social care | 2020 |
| Dispite Finans & IT Nuf | Professional & scientific | 2023 |
| Djbutikken AS | Wholesale & retail | 2021 |
| DJM Invest AS | | 2026 |
| DL Eiendom AS | Real estate | 2012 |
| Dmw-Solfilm Da | Construction | 2010 |
| Dog Consult AS | Other services | 2012 |
| Dolva AS | Health & social care | 1991 |
| Don'T Look Back AS | | 2023 |
| Dragon Holding AS | Real estate | 2007 |
| Driftsteknikk Eiendom AS | Real estate | 2008 |
| Drivhuset Blomster Ans | Wholesale & retail | 1990 |
| Drone Operatøren Nuf | Professional & scientific | 2020 |
| Dualo AS | Wholesale & retail | 2019 |
| Dunamis Technology AS | Information & communication | 2019 |
| DVK Holding AS | | 2021 |
| DW Consulting AS | Information & communication | 2010 |
| Dwteknikk AS | Mining & quarrying | 2003 |
| Dyreparadiset AS | Wholesale & retail | 2021 |
| Dør & Vindu Halden AS | Wholesale & retail | 2013 |
| E&E Invest AS | | 2019 |
| E-Helsekonsulenten AS | Professional & scientific | 2019 |
| E6 Svinesund 1 AS | Real estate | 2020 |
| E6 Svinesund 2 AS | Real estate | 2020 |
| E6 Svinesund 3 AS | Real estate | 2019 |
| E6 Svinesund 4 AS | Real estate | 2019 |
| E6 Svinesund 5 AS | Real estate | 2019 |
| Eagle Holding AS | | 2024 |
| Eagle Technology AS | Manufacturing | 2025 |
| Ebor Invest AS | Financial services | 2012 |
| Ebro Eiendom AS | Real estate | 1999 |
| Ecapital AS | Real estate | 2000 |
| Ecapital Consulting AS | Professional & scientific | 2005 |
| Ecapital Eiendom AS | Real estate | 2005 |
| Eclectic AS | Manufacturing | 2017 |
| Ecomhub AS | | 2024 |
| Edge of Nature AS | Wholesale & retail | 2025 |
| Edvardsen Holding AS | Real estate | 2010 |
| Eiendom Torvet AS | Real estate | 2020 |
| Eiendoms-Gruppen AS | Construction | 2020 |
| Eiendomsselskapet RV 14 AS | Wholesale & retail | 1989 |
| Eiendomsteam Da | Real estate | 2007 |
| Eira Omsorg AS | Health & social care | 2026 |
| Ek Rengjøring Og Vedlikehold AS | Administrative & support | 2021 |
| Ekanor AS | Real estate | 2026 |
| Ekonect AS | Information & communication | 2020 |
| Ekonect Invest AS | | 2020 |
| El-Smart Installasjon AS | Construction | 2018 |
| Elastikk AS | Information & communication | 2025 |
| Elektrikertjenesten Halden AS | Construction | 2003 |
| Elektrovakuum AS | Wholesale & retail | 2001 |
| Elisenberg Elektro AS | Construction | 2017 |
| Elkontroll Øst AS | Professional & scientific | 2014 |