| Hyko Invest AS | Wholesale & retail | 2007 |
| Hylleselskap Ingen Aktivitet AS | | 2018 |
| Hyni Bygg AS | Construction | 1992 |
| Henrik Ibsensgate 6 AS | Real estate | 1978 |
| Hågasletta 11 AS | Real estate | 2022 |
| Hår AS | Other services | 2005 |
| Hårekspressen Ans | Other services | 1990 |
| Hårgrossisten AS | Other services | 2005 |
| Håvundvegen 261 AS | Real estate | 2013 |
| Håvundvegen Næringspark AS | Real estate | 2006 |
| Håvundveien 214 AS | Real estate | 2019 |
| Håøya Og Auenlandet Utbyggingsselskap SA | Construction | 2019 |
| Håøya Og Auenlandet Vann Og Avløp SA | Water & waste | 2019 |
| Höganäs Borgestad AS | Manufacturing | 1974 |
| Høgli Maskin AS | Construction | 2019 |
| Høsbjørnvegen 2 AS | Real estate | 2019 |
| Høsbjørvegen 2C AS | Real estate | 2019 |
| Høyanfjellet 10 AS | Professional & scientific | 2017 |
| Høyanfjellet Holding AS | Real estate | 2005 |
| Høyanfjellet Invest AS | Real estate | 2021 |
| Høydalsmovegen 807 AS | Real estate | 2022 |
| Høyergruppen AS | Transport & logistics | 2017 |
| Høyerinvest AS | | 2022 |
| Høyt & Lavt Multitjenester Skien AS | Administrative & support | 2024 |
| Ibsen Gruppen AS | Real estate | 2010 |
| Ibsen Tannlegesenter AS | Health & social care | 2014 |
| Ibsenbusiness AS | Professional & scientific | 2000 |
| Ibsenhuset AS | Arts & recreation | 1971 |
| Icare Medical AS | Wholesale & retail | 2013 |
| Icecon Nordic AS | Professional & scientific | 2026 |
| Icon Invest AS | Professional & scientific | 2010 |
| ID4YOU AS | Wholesale & retail | 2004 |
| Idathe Holding AS | | 2026 |
| Ide Maling Og Arbeidssenter Da | Health & social care | 1997 |
| Idyllisk AS | Wholesale & retail | 2013 |
| Iform Skien AS | Arts & recreation | 2022 |
| Ikab AS | Wholesale & retail | 1977 |
| Ikab Holding AS | | 2026 |
| Ikab Invest AS | | 2026 |
| Ikasala AS | Other services | 2024 |
| Ilarsen AS | Construction | 2025 |
| Ildvorn AS | Professional & scientific | 2021 |
| Illing Invest AS | | 2023 |
| Illyrian Auto AS | Wholesale & retail | 2023 |
| Illyrian Invest AS | Wholesale & retail | 2023 |
| Imed AS | Health & social care | 2013 |
| Imingbruddet AS | Real estate | 2024 |
| Imobiliare Holding AS | Other services | 2022 |
| Imperium Marketing AS | | 2026 |
| Inanis AS | Real estate | 2016 |
| Incumedic AS | | 2019 |
| Indian Summer Da | Arts & recreation | 2006 |
| Induction Holding AS | Manufacturing | 2021 |
| Industrikompetanse Da | Wholesale & retail | 2002 |
| Industristål AS | Wholesale & retail | 2015 |
| Informedia AS | Professional & scientific | 1994 |
| Ing Kjell a Sletten AS | Real estate | 1994 |
| Ingma Holding AS | | 2018 |
| Initial Holding AS | Professional & scientific | 2012 |
| Innesving AS | Arts & recreation | 2025 |
| Innovapro AS | Professional & scientific | 2015 |
| Innredningshjelpen AS | Professional & scientific | 2023 |
| Innveier AS | Education | 2025 |
| Inorge AS | Information & communication | 2018 |
| Insilva Holding AS | Information & communication | 2022 |
| Inspiro Life Coaching AS | Real estate | 2007 |
| Institutt for Psykologi Og Sexologi AS | Health & social care | 2013 |
| Intentive AS | Wholesale & retail | 2024 |
| Intero AS | Real estate | 2019 |
| Intersource Norway AS | Wholesale & retail | 2025 |
| Inti Ren AS | Administrative & support | 2021 |
| Intvest Bølevegen 63A AS | Real estate | 2006 |
| Invencubation AS | Professional & scientific | 2008 |
| Inventum Norge AS | Wholesale & retail | 2019 |
| Invest BSS Skien AS | Wholesale & retail | 1999 |
| Invest SRG Grenland AS | Real estate | 1999 |
| Invest Warde AS | | 1998 |
| Investa - AS | Real estate | 2021 |
| Investa Utvikling AS | Construction | 2004 |
| Investart AS | Real estate | 2020 |
| Investia AS | Real estate | 2022 |
| Investium AS | Real estate | 2015 |
| Invezt AS | | 2023 |
| Ipahla Invest AS | Real estate | 2005 |
| Ipsum Regnskap AS | Professional & scientific | 2017 |
| Irato AS | | 2025 |
| Isa Service Solutions Holding AS | | 2025 |
| Isak M. Nilsen AS | Professional & scientific | 2005 |
| Isaksen Vedlikehold AS | Administrative & support | 2011 |
| Isdammen AS | Real estate | 2008 |
| Iskufilan Shop AS | Wholesale & retail | 2025 |
| Isme Holding AS | Wholesale & retail | 2025 |
| Iso Management AS | Professional & scientific | 2016 |
| Isonor Construction AS | Professional & scientific | 2017 |
| Isortoq AS | Professional & scientific | 2023 |
| Itron AS | Professional & scientific | 2026 |
| J Johansens Rengjøringsbyrå AS | Administrative & support | 1999 |
| J Torsnes Holding AS | Construction | 2019 |
| J&L Utvikling AS | Real estate | 2021 |
| J-Bygg AS | Construction | 2021 |